SubjectExecutor.ts

import {SapDriver} from "../driver/sap/SapDriver";
import {QueryRunner} from "../query-runner/QueryRunner";
import {Subject} from "./Subject";
import {SubjectTopoligicalSorter} from "./SubjectTopoligicalSorter";
import {SubjectChangedColumnsComputer} from "./SubjectChangedColumnsComputer";
import {SubjectWithoutIdentifierError} from "../error/SubjectWithoutIdentifierError";
import {SubjectRemovedAndUpdatedError} from "../error/SubjectRemovedAndUpdatedError";
import {MongoQueryRunner} from "../driver/mongodb/MongoQueryRunner";
import {MongoEntityManager} from "../entity-manager/MongoEntityManager";
import {MongoDriver} from "../driver/mongodb/MongoDriver";
import {ObjectLiteral} from "../common/ObjectLiteral";
import {SaveOptions} from "../repository/SaveOptions";
import {RemoveOptions} from "../repository/RemoveOptions";
import {BroadcasterResult} from "../subscriber/BroadcasterResult";
import {OracleDriver} from "../driver/oracle/OracleDriver";
import {NestedSetSubjectExecutor} from "./tree/NestedSetSubjectExecutor";
import {ClosureSubjectExecutor} from "./tree/ClosureSubjectExecutor";
import {MaterializedPathSubjectExecutor} from "./tree/MaterializedPathSubjectExecutor";
import {OrmUtils} from "../util/OrmUtils";

/**
 * Executes all database operations (inserts, updated, deletes) that must be executed
 * with given persistence subjects.
 */
export class SubjectExecutor {

    // -------------------------------------------------------------------------
    // Public Properties
    // -------------------------------------------------------------------------

    /**
     * Indicates if executor has any operations to execute (e.g. has insert / update / delete operations to be executed).
     */
    hasExecutableOperations: boolean = false;

    // -------------------------------------------------------------------------
    // Protected Properties
    // -------------------------------------------------------------------------

    /**
     * QueryRunner used to execute all queries with a given subjects.
     */
    protected queryRunner: QueryRunner;

    /**
     * Persistence options.
     */
    protected options?: SaveOptions & RemoveOptions;

    /**
     * All subjects that needs to be operated.
     */
    protected allSubjects: Subject[];

    /**
     * Subjects that must be inserted.
     */
    protected insertSubjects: Subject[] = [];

    /**
     * Subjects that must be updated.
     */
    protected updateSubjects: Subject[] = [];

    /**
     * Subjects that must be removed.
     */
    protected removeSubjects: Subject[] = [];

    /**
     * Subjects that must be soft-removed.
     */
    protected softRemoveSubjects: Subject[] = [];

    /**
     * Subjects that must be recovered.
     */
    protected recoverSubjects: Subject[] = [];

    // -------------------------------------------------------------------------
    // Constructor
    // -------------------------------------------------------------------------

    constructor(queryRunner: QueryRunner, subjects: Subject[], options?: SaveOptions & RemoveOptions) {
        this.queryRunner = queryRunner;
        this.allSubjects = subjects;
        this.options = options;
        this.validate();
        this.recompute();
    }

    // -------------------------------------------------------------------------
    // Public Methods
    // -------------------------------------------------------------------------

    /**
     * Executes all operations over given array of subjects.
     * Executes queries using given query runner.
     */
    async execute(): Promise<void> {
        // console.time("SubjectExecutor.execute");

        // broadcast "before" events before we start insert / update / remove operations
        let broadcasterResult: BroadcasterResult | undefined = undefined;
        if (!this.options || this.options.listeners !== false) {
            // console.time(".broadcastBeforeEventsForAll");
            broadcasterResult = this.broadcastBeforeEventsForAll();
            if (broadcasterResult.promises.length > 0) await Promise.all(broadcasterResult.promises);
            // console.timeEnd(".broadcastBeforeEventsForAll");
        }

        // since event listeners and subscribers can call save methods and/or trigger entity changes we need to recompute operational subjects
        // recompute only in the case if any listener or subscriber was really executed
        if (broadcasterResult && broadcasterResult.count > 0) {
            // console.time(".recompute");
            this.insertSubjects.forEach(subject => subject.recompute());
            this.updateSubjects.forEach(subject => subject.recompute());
            this.removeSubjects.forEach(subject => subject.recompute());
            this.softRemoveSubjects.forEach(subject => subject.recompute());
            this.recoverSubjects.forEach(subject => subject.recompute());
            this.recompute();
            // console.timeEnd(".recompute");
        }

        // make sure our insert subjects are sorted (using topological sorting) to make cascade inserts work properly

        // console.timeEnd("prepare");

        // execute all insert operations
        // console.time(".insertion");
        this.insertSubjects = new SubjectTopoligicalSorter(this.insertSubjects).sort("insert");
        await this.executeInsertOperations();
        // console.timeEnd(".insertion");

        // recompute update operations since insertion can create updation operations for the
        // properties it wasn't able to handle on its own (referenced columns)
        this.updateSubjects = this.allSubjects.filter(subject => subject.mustBeUpdated);

        // execute update operations
        // console.time(".updation");
        await this.executeUpdateOperations();
        // console.timeEnd(".updation");

        // make sure our remove subjects are sorted (using topological sorting) when multiple entities are passed for the removal
        // console.time(".removal");
        this.removeSubjects = new SubjectTopoligicalSorter(this.removeSubjects).sort("delete");
        await this.executeRemoveOperations();
        // console.timeEnd(".removal");

        // recompute soft-remove operations
        this.softRemoveSubjects = this.allSubjects.filter(subject => subject.mustBeSoftRemoved);

        // execute soft-remove operations
        await this.executeSoftRemoveOperations();

        // recompute recover operations
        this.recoverSubjects = this.allSubjects.filter(subject => subject.mustBeRecovered);

        // execute recover operations
        await this.executeRecoverOperations();

        // update all special columns in persisted entities, like inserted id or remove ids from the removed entities
        // console.time(".updateSpecialColumnsInPersistedEntities");
        await this.updateSpecialColumnsInPersistedEntities();
        // console.timeEnd(".updateSpecialColumnsInPersistedEntities");

        // finally broadcast "after" events after we finish insert / update / remove operations
        if (!this.options || this.options.listeners !== false) {
            // console.time(".broadcastAfterEventsForAll");
            broadcasterResult = this.broadcastAfterEventsForAll();
            if (broadcasterResult.promises.length > 0) await Promise.all(broadcasterResult.promises);
            // console.timeEnd(".broadcastAfterEventsForAll");
        }
        // console.timeEnd("SubjectExecutor.execute");
    }

    // -------------------------------------------------------------------------
    // Protected Methods
    // -------------------------------------------------------------------------

    /**
     * Validates all given subjects.
     */
    protected validate() {
        this.allSubjects.forEach(subject => {
            if (subject.mustBeUpdated && subject.mustBeRemoved)
                throw new SubjectRemovedAndUpdatedError(subject);
        });
    }

    /**
     * Performs entity re-computations - finds changed columns, re-builds insert/update/remove subjects.
     */
    protected recompute(): void {
        new SubjectChangedColumnsComputer().compute(this.allSubjects);
        this.insertSubjects = this.allSubjects.filter(subject => subject.mustBeInserted);
        this.updateSubjects = this.allSubjects.filter(subject => subject.mustBeUpdated);
        this.removeSubjects = this.allSubjects.filter(subject => subject.mustBeRemoved);
        this.softRemoveSubjects = this.allSubjects.filter(subject => subject.mustBeSoftRemoved);
        this.recoverSubjects = this.allSubjects.filter(subject => subject.mustBeRecovered);
        this.hasExecutableOperations = this.insertSubjects.length > 0 || this.updateSubjects.length > 0 || this.removeSubjects.length > 0 || this.softRemoveSubjects.length > 0 || this.recoverSubjects.length > 0;
    }

    /**
     * Broadcasts "BEFORE_INSERT", "BEFORE_UPDATE", "BEFORE_REMOVE" events for all given subjects.
     */
    protected broadcastBeforeEventsForAll(): BroadcasterResult {
        const result = new BroadcasterResult();
        if (this.insertSubjects.length)
            this.insertSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastBeforeInsertEvent(result, subject.metadata, subject.entity!));
        if (this.updateSubjects.length)
            this.updateSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastBeforeUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        if (this.removeSubjects.length)
            this.removeSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastBeforeRemoveEvent(result, subject.metadata, subject.entity!, subject.databaseEntity));
        if (this.softRemoveSubjects.length)
            this.softRemoveSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastBeforeUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        if (this.recoverSubjects.length)
            this.recoverSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastBeforeUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        return result;
    }

    /**
     * Broadcasts "AFTER_INSERT", "AFTER_UPDATE", "AFTER_REMOVE" events for all given subjects.
     * Returns void if there wasn't any listener or subscriber executed.
     * Note: this method has a performance-optimized code organization.
     */
    protected broadcastAfterEventsForAll(): BroadcasterResult {
        const result = new BroadcasterResult();
        if (this.insertSubjects.length)
            this.insertSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastAfterInsertEvent(result, subject.metadata, subject.entity!));
        if (this.updateSubjects.length)
            this.updateSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastAfterUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        if (this.removeSubjects.length)
            this.removeSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastAfterRemoveEvent(result, subject.metadata, subject.entity!, subject.databaseEntity));
        if (this.softRemoveSubjects.length)
            this.softRemoveSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastAfterUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        if (this.recoverSubjects.length)
            this.recoverSubjects.forEach(subject => this.queryRunner.broadcaster.broadcastAfterUpdateEvent(result, subject.metadata, subject.entity!, subject.databaseEntity, subject.diffColumns, subject.diffRelations));
        return result;
    }

    /**
     * Executes insert operations.
     */
    protected async executeInsertOperations(): Promise<void> {
        // group insertion subjects to make bulk insertions
        const [groupedInsertSubjects, groupedInsertSubjectKeys] = this.groupBulkSubjects(this.insertSubjects, "insert");

        // then we run insertion in the sequential order which is important since we have an ordered subjects
        for (const groupName of groupedInsertSubjectKeys) {
            const subjects = groupedInsertSubjects[groupName];

            // we must separately insert entities which does not have any values to insert
            // because its not possible to insert multiple entities with only default values in bulk
            const bulkInsertMaps: ObjectLiteral[] = [];
            const bulkInsertSubjects: Subject[] = [];
            const singleInsertSubjects: Subject[] = [];
            if (this.queryRunner.connection.driver instanceof MongoDriver) {
                subjects.forEach(subject => {
                    if (subject.metadata.createDateColumn && subject.entity) {
                        subject.entity[subject.metadata.createDateColumn.databaseName] = new Date();
                    }

                    if (subject.metadata.updateDateColumn && subject.entity) {
                        subject.entity[subject.metadata.updateDateColumn.databaseName] = new Date();
                    }

                    subject.createValueSetAndPopChangeMap();

                    bulkInsertSubjects.push(subject);
                    bulkInsertMaps.push(subject.entity!);
                });
            } else if (this.queryRunner.connection.driver instanceof OracleDriver) {
                subjects.forEach(subject => {
                    singleInsertSubjects.push(subject);
                });
            } else {
                subjects.forEach(subject => {

                    // we do not insert in bulk in following cases:
                    // - when there is no values in insert (only defaults are inserted), since we cannot use DEFAULT VALUES expression for multiple inserted rows
                    // - when entity is a tree table, since tree tables require extra operation per each inserted row
                    // - when oracle is used, since oracle's bulk insertion is very bad
                    if (subject.changeMaps.length === 0 ||
                        subject.metadata.treeType ||
                        this.queryRunner.connection.driver instanceof OracleDriver ||
                        this.queryRunner.connection.driver instanceof SapDriver) {
                        singleInsertSubjects.push(subject);

                    } else {
                        bulkInsertSubjects.push(subject);
                        bulkInsertMaps.push(subject.createValueSetAndPopChangeMap());
                    }
                });
            }

            // for mongodb we have a bit different insertion logic
            if (this.queryRunner instanceof MongoQueryRunner) {
                const manager = this.queryRunner.manager as MongoEntityManager;
                const insertResult = await manager.insert(subjects[0].metadata.target, bulkInsertMaps);
                subjects.forEach((subject, index) => {
                    subject.identifier = insertResult.identifiers[index];
                    subject.generatedMap = insertResult.generatedMaps[index];
                    subject.insertedValueSet = bulkInsertMaps[index];
                });

            } else {

                // here we execute our insertion query
                // we need to enable entity updation because we DO need to have updated insertedMap
                // which is not same object as our entity that's why we don't need to worry about our entity to get dirty
                // also, we disable listeners because we call them on our own in persistence layer
                if (bulkInsertMaps.length > 0) {
                    const insertResult = await this.queryRunner
                        .manager
                        .createQueryBuilder()
                        .insert()
                        .into(subjects[0].metadata.target)
                        .values(bulkInsertMaps)
                        .updateEntity(this.options && this.options.reload === false ? false : true)
                        .callListeners(false)
                        .execute();

                    bulkInsertSubjects.forEach((subject, index) => {
                        subject.identifier = insertResult.identifiers[index];
                        subject.generatedMap = insertResult.generatedMaps[index];
                        subject.insertedValueSet = bulkInsertMaps[index];
                    });
                }

                // insert subjects which must be inserted in separate requests (all default values)
                if (singleInsertSubjects.length > 0) {
                    for (const subject of singleInsertSubjects) {
                        subject.insertedValueSet = subject.createValueSetAndPopChangeMap(); // important to have because query builder sets inserted values into it

                        // for nested set we execute additional queries
                        if (subject.metadata.treeType === "nested-set")
                            await new NestedSetSubjectExecutor(this.queryRunner).insert(subject);

                        await this.queryRunner
                            .manager
                            .createQueryBuilder()
                            .insert()
                            .into(subject.metadata.target)
                            .values(subject.insertedValueSet)
                            .updateEntity(this.options && this.options.reload === false ? false : true)
                            .callListeners(false)
                            .execute()
                            .then(insertResult => {
                                subject.identifier = insertResult.identifiers[0];
                                subject.generatedMap = insertResult.generatedMaps[0];
                            });

                        // for tree tables we execute additional queries
                        if (subject.metadata.treeType === "closure-table") {
                            await new ClosureSubjectExecutor(this.queryRunner).insert(subject);

                        } else if (subject.metadata.treeType === "materialized-path") {
                            await new MaterializedPathSubjectExecutor(this.queryRunner).insert(subject);
                        }
                    }
                }
            }

            subjects.forEach(subject => {
                if (subject.generatedMap) {
                    subject.metadata.columns.forEach(column => {
                        const value = column.getEntityValue(subject.generatedMap!);
                        if (value !== undefined && value !== null) {
                            const preparedValue = this.queryRunner.connection.driver.prepareHydratedValue(value, column);
                            column.setEntityValue(subject.generatedMap!, preparedValue);
                        }
                    });
                }
            });
        }
    }

    /**
     * Updates all given subjects in the database.
     */
    protected async executeUpdateOperations(): Promise<void> {
        const updateSubject = async (subject: Subject) => {

            if (!subject.identifier)
                throw new SubjectWithoutIdentifierError(subject);

            // for mongodb we have a bit different updation logic
            if (this.queryRunner instanceof MongoQueryRunner) {
                const partialEntity = this.cloneMongoSubjectEntity(subject);
                if (subject.metadata.objectIdColumn && subject.metadata.objectIdColumn.propertyName) {
                    delete partialEntity[subject.metadata.objectIdColumn.propertyName];
                }

                if (subject.metadata.createDateColumn && subject.metadata.createDateColumn.propertyName) {
                    delete partialEntity[subject.metadata.createDateColumn.propertyName];
                }

                if (subject.metadata.updateDateColumn && subject.metadata.updateDateColumn.propertyName) {
                    partialEntity[subject.metadata.updateDateColumn.propertyName] = new Date();
                }

                const manager = this.queryRunner.manager as MongoEntityManager;

                await manager.update(subject.metadata.target, subject.identifier, partialEntity);

            } else {

                const updateMap: ObjectLiteral = subject.createValueSetAndPopChangeMap();

                // for tree tables we execute additional queries
                switch (subject.metadata.treeType) {
                    case "nested-set":
                        await new NestedSetSubjectExecutor(this.queryRunner).update(subject);
                        break;

                    case "closure-table":
                        await new ClosureSubjectExecutor(this.queryRunner).update(subject);
                        break;

                    case "materialized-path":
                        await new MaterializedPathSubjectExecutor(this.queryRunner).update(subject);
                        break;
                }

                // here we execute our updation query
                // we need to enable entity updation because we update a subject identifier
                // which is not same object as our entity that's why we don't need to worry about our entity to get dirty
                // also, we disable listeners because we call them on our own in persistence layer
                const updateQueryBuilder = this.queryRunner
                    .manager
                    .createQueryBuilder()
                    .update(subject.metadata.target)
                    .set(updateMap)
                    .updateEntity(this.options && this.options.reload === false ? false : true)
                    .callListeners(false);

                if (subject.entity) {
                    updateQueryBuilder.whereEntity(subject.identifier);

                } else { // in this case identifier is just conditions object to update by
                    updateQueryBuilder.where(subject.identifier);
                }

                const updateResult = await updateQueryBuilder.execute();
                let updateGeneratedMap = updateResult.generatedMaps[0];
                if (updateGeneratedMap) {
                    subject.metadata.columns.forEach(column => {
                        const value = column.getEntityValue(updateGeneratedMap!);
                        if (value !== undefined && value !== null) {
                            const preparedValue = this.queryRunner.connection.driver.prepareHydratedValue(value, column);
                            column.setEntityValue(updateGeneratedMap!, preparedValue);
                        }
                    });
                    if (!subject.generatedMap) {
                        subject.generatedMap = {};
                    }
                    Object.assign(subject.generatedMap, updateGeneratedMap);
                }
            }
        };

        // Nested sets need to be updated one by one
        // Split array in two, one with nested set subjects and the other with the remaining subjects
        const nestedSetSubjects: Subject[] = [];
        const remainingSubjects: Subject[] = [];

        for (const subject of this.updateSubjects) {
            if (subject.metadata.treeType === "nested-set") {
                nestedSetSubjects.push(subject);
            } else {
                remainingSubjects.push(subject);
            }
        }

        // Run nested set updates one by one
        const nestedSetPromise = new Promise<void>(async (resolve, reject) => {
            for (const subject of nestedSetSubjects) {
                try {
                    await updateSubject(subject);
                } catch (error) {
                    reject(error);
                }
            }
            resolve();
        });

        // Run all remaning subjects in parallel
        await Promise.all([...remainingSubjects.map(updateSubject), nestedSetPromise]);
    }

    /**
     * Removes all given subjects from the database.
     *
     * todo: we need to apply topological sort here as well
     */
    protected async executeRemoveOperations(): Promise<void> {
        // group insertion subjects to make bulk insertions
        const [groupedRemoveSubjects, groupedRemoveSubjectKeys] = this.groupBulkSubjects(this.removeSubjects, "delete");

        for (const groupName of groupedRemoveSubjectKeys) {
            const subjects = groupedRemoveSubjects[groupName];
            const deleteMaps = subjects.map(subject => {
                if (!subject.identifier)
                    throw new SubjectWithoutIdentifierError(subject);

                return subject.identifier;
            });

            // for mongodb we have a bit different updation logic
            if (this.queryRunner instanceof MongoQueryRunner) {
                const manager = this.queryRunner.manager as MongoEntityManager;
                await manager.delete(subjects[0].metadata.target, deleteMaps);

            } else {
                // for tree tables we execute additional queries
                switch (subjects[0].metadata.treeType) {
                    case "nested-set":
                        await new NestedSetSubjectExecutor(this.queryRunner).remove(subjects);
                        break;

                    case "closure-table":
                        await new ClosureSubjectExecutor(this.queryRunner).remove(subjects);
                        break;
                }

                // here we execute our deletion query
                // we don't need to specify entities and set update entity to true since the only thing query builder
                // will do for use is a primary keys deletion which is handled by us later once persistence is finished
                // also, we disable listeners because we call them on our own in persistence layer
                await this.queryRunner
                    .manager
                    .createQueryBuilder()
                    .delete()
                    .from(subjects[0].metadata.target)
                    .where(deleteMaps)
                    .callListeners(false)
                    .execute();
            }
        }
    }

    private cloneMongoSubjectEntity(subject: Subject): ObjectLiteral {
        const target: ObjectLiteral = {};

        if (subject.entity) {
            for (const column of subject.metadata.columns) {
                OrmUtils.mergeDeep(target, column.getEntityValueMap(subject.entity));
            }
        }

        return target;
    }

    /**
     * Soft-removes all given subjects in the database.
     */
    protected async executeSoftRemoveOperations(): Promise<void> {
        await Promise.all(this.softRemoveSubjects.map(async subject => {

            if (!subject.identifier)
                throw new SubjectWithoutIdentifierError(subject);

            // for mongodb we have a bit different updation logic
            if (this.queryRunner instanceof MongoQueryRunner) {
                const partialEntity = this.cloneMongoSubjectEntity(subject);
                if (subject.metadata.objectIdColumn && subject.metadata.objectIdColumn.propertyName) {
                    delete partialEntity[subject.metadata.objectIdColumn.propertyName];
                }

                if (subject.metadata.createDateColumn && subject.metadata.createDateColumn.propertyName) {
                    delete partialEntity[subject.metadata.createDateColumn.propertyName];
                }

                if (subject.metadata.updateDateColumn && subject.metadata.updateDateColumn.propertyName) {
                    partialEntity[subject.metadata.updateDateColumn.propertyName] = new Date();
                }

                if (subject.metadata.deleteDateColumn && subject.metadata.deleteDateColumn.propertyName) {
                    partialEntity[subject.metadata.deleteDateColumn.propertyName] = new Date();
                }

                const manager = this.queryRunner.manager as MongoEntityManager;

                await manager.update(subject.metadata.target, subject.identifier, partialEntity);

            } else {

                // here we execute our soft-deletion query
                // we need to enable entity soft-deletion because we update a subject identifier
                // which is not same object as our entity that's why we don't need to worry about our entity to get dirty
                // also, we disable listeners because we call them on our own in persistence layer
                const softDeleteQueryBuilder = this.queryRunner
                    .manager
                    .createQueryBuilder()
                    .softDelete()
                    .from(subject.metadata.target)
                    .updateEntity(this.options && this.options.reload === false ? false : true)
                    .callListeners(false);

                if (subject.entity) {
                    softDeleteQueryBuilder.whereEntity(subject.identifier);

                } else { // in this case identifier is just conditions object to update by
                    softDeleteQueryBuilder.where(subject.identifier);
                }

                const updateResult = await softDeleteQueryBuilder.execute();
                subject.generatedMap = updateResult.generatedMaps[0];
                if (subject.generatedMap) {
                    subject.metadata.columns.forEach(column => {
                        const value = column.getEntityValue(subject.generatedMap!);
                        if (value !== undefined && value !== null) {
                            const preparedValue = this.queryRunner.connection.driver.prepareHydratedValue(value, column);
                            column.setEntityValue(subject.generatedMap!, preparedValue);
                        }
                    });
                }

                // experiments, remove probably, need to implement tree tables children removal
                // if (subject.updatedRelationMaps.length > 0) {
                //     await Promise.all(subject.updatedRelationMaps.map(async updatedRelation => {
                //         if (!updatedRelation.relation.isTreeParent) return;
                //         if (!updatedRelation.value !== null) return;
                //
                //         if (subject.metadata.treeType === "closure-table") {
                //             await new ClosureSubjectExecutor(this.queryRunner).deleteChildrenOf(subject);
                //         }
                //     }));
                // }
            }
        }));
    }

    /**
     * Recovers all given subjects in the database.
     */
    protected async executeRecoverOperations(): Promise<void> {
        await Promise.all(this.recoverSubjects.map(async subject => {

            if (!subject.identifier)
                throw new SubjectWithoutIdentifierError(subject);

            // for mongodb we have a bit different updation logic
            if (this.queryRunner instanceof MongoQueryRunner) {
                const partialEntity = this.cloneMongoSubjectEntity(subject);
                if (subject.metadata.objectIdColumn && subject.metadata.objectIdColumn.propertyName) {
                    delete partialEntity[subject.metadata.objectIdColumn.propertyName];
                }

                if (subject.metadata.createDateColumn && subject.metadata.createDateColumn.propertyName) {
                    delete partialEntity[subject.metadata.createDateColumn.propertyName];
                }

                if (subject.metadata.updateDateColumn && subject.metadata.updateDateColumn.propertyName) {
                    partialEntity[subject.metadata.updateDateColumn.propertyName] = new Date();
                }

                if (subject.metadata.deleteDateColumn && subject.metadata.deleteDateColumn.propertyName) {
                    partialEntity[subject.metadata.deleteDateColumn.propertyName] = null;
                }

                const manager = this.queryRunner.manager as MongoEntityManager;

                await manager.update(subject.metadata.target, subject.identifier, partialEntity);

            } else {

                // here we execute our restory query
                // we need to enable entity restory because we update a subject identifier
                // which is not same object as our entity that's why we don't need to worry about our entity to get dirty
                // also, we disable listeners because we call them on our own in persistence layer
                const softDeleteQueryBuilder = this.queryRunner
                    .manager
                    .createQueryBuilder()
                    .restore()
                    .from(subject.metadata.target)
                    .updateEntity(this.options && this.options.reload === false ? false : true)
                    .callListeners(false);

                if (subject.entity) {
                    softDeleteQueryBuilder.whereEntity(subject.identifier);

                } else { // in this case identifier is just conditions object to update by
                    softDeleteQueryBuilder.where(subject.identifier);
                }

                const updateResult = await softDeleteQueryBuilder.execute();
                subject.generatedMap = updateResult.generatedMaps[0];
                if (subject.generatedMap) {
                    subject.metadata.columns.forEach(column => {
                        const value = column.getEntityValue(subject.generatedMap!);
                        if (value !== undefined && value !== null) {
                            const preparedValue = this.queryRunner.connection.driver.prepareHydratedValue(value, column);
                            column.setEntityValue(subject.generatedMap!, preparedValue);
                        }
                    });
                }

                // experiments, remove probably, need to implement tree tables children removal
                // if (subject.updatedRelationMaps.length > 0) {
                //     await Promise.all(subject.updatedRelationMaps.map(async updatedRelation => {
                //         if (!updatedRelation.relation.isTreeParent) return;
                //         if (!updatedRelation.value !== null) return;
                //
                //         if (subject.metadata.treeType === "closure-table") {
                //             await new ClosureSubjectExecutor(this.queryRunner).deleteChildrenOf(subject);
                //         }
                //     }));
                // }
            }
        }));
    }

    /**
     * Updates all special columns of the saving entities (create date, update date, version, etc.).
     * Also updates nullable columns and columns with default values.
     */
    protected updateSpecialColumnsInPersistedEntities(): void {

        // update inserted entity properties
        if (this.insertSubjects.length)
            this.updateSpecialColumnsInInsertedAndUpdatedEntities(this.insertSubjects);

        // update updated entity properties
        if (this.updateSubjects.length)
            this.updateSpecialColumnsInInsertedAndUpdatedEntities(this.updateSubjects);

        // update soft-removed entity properties
        if (this.updateSubjects.length)
            this.updateSpecialColumnsInInsertedAndUpdatedEntities(this.softRemoveSubjects);

        // update recovered entity properties
        if (this.updateSubjects.length)
            this.updateSpecialColumnsInInsertedAndUpdatedEntities(this.recoverSubjects);

        // remove ids from the entities that were removed
        if (this.removeSubjects.length) {
            this.removeSubjects.forEach(subject => {
                if (!subject.entity) return;

                subject.metadata.primaryColumns.forEach(primaryColumn => {
                    primaryColumn.setEntityValue(subject.entity!, undefined);
                });
            });
        }

        // other post-persist updations
        this.allSubjects.forEach(subject => {
            if (!subject.entity) return;

            subject.metadata.relationIds.forEach(relationId => {
                relationId.setValue(subject.entity!);
            });

            // mongo _id remove
            if (this.queryRunner instanceof MongoQueryRunner) {
                if (subject.metadata.objectIdColumn
                    && subject.metadata.objectIdColumn.databaseName
                    && subject.metadata.objectIdColumn.databaseName !== subject.metadata.objectIdColumn.propertyName
                ) {
                    delete subject.entity[subject.metadata.objectIdColumn.databaseName];
                }
            }
        });
    }

    /**
     * Updates all special columns of the saving entities (create date, update date, version, etc.).
     * Also updates nullable columns and columns with default values.
     */
    protected updateSpecialColumnsInInsertedAndUpdatedEntities(subjects: Subject[]): void {
        subjects.forEach(subject => {
            if (!subject.entity) return;

            // set values to "null" for nullable columns that did not have values
            subject.metadata.columns.forEach(column => {

                // if table inheritance is used make sure this column is not child's column
                if (subject.metadata.childEntityMetadatas.length > 0 && subject.metadata.childEntityMetadatas.map(metadata => metadata.target).indexOf(column.target) !== -1)
                    return;

                // entities does not have virtual columns
                if (column.isVirtual)
                    return;

                // update nullable columns
                if (column.isNullable) {
                    const columnValue = column.getEntityValue(subject.entity!);
                    if (columnValue === undefined)
                        column.setEntityValue(subject.entity!, null);
                }

                // update relational columns
                if (subject.updatedRelationMaps.length > 0) {
                    subject.updatedRelationMaps.forEach(updatedRelationMap => {
                        updatedRelationMap.relation.joinColumns.forEach(column => {
                            if (column.isVirtual === true)
                                return;

                            column.setEntityValue(subject.entity!, updatedRelationMap.value instanceof Object ? column.referencedColumn!.getEntityValue(updatedRelationMap.value) : updatedRelationMap.value);
                        });
                    });
                }
            });

            // merge into entity all generated values returned by a database
            if (subject.generatedMap)
                this.queryRunner.manager.merge(subject.metadata.target as any, subject.entity, subject.generatedMap);
        });
    }

    /**
     * Groups subjects by metadata names (by tables) to make bulk insertions and deletions possible.
     * However there are some limitations with bulk insertions of data into tables with generated (increment) columns
     * in some drivers. Some drivers like mysql and sqlite does not support returning multiple generated columns
     * after insertion and can only return a single generated column value, that's why its not possible to do bulk insertion,
     * because it breaks insertion result's generatedMap and leads to problems when this subject is used in other subjects saves.
     * That's why we only support bulking in junction tables for those drivers.
     *
     * Other drivers like postgres and sql server support RETURNING / OUTPUT statement which allows to return generated
     * id for each inserted row, that's why bulk insertion is not limited to junction tables in there.
     */
    protected groupBulkSubjects(subjects: Subject[], type: "insert" | "delete"): [{ [key: string]: Subject[] }, string[]] {
        const group: { [key: string]: Subject[] } = {};
        const keys: string[] = [];
        const groupingAllowed = type === "delete" || this.queryRunner.connection.driver.isReturningSqlSupported();

        subjects.forEach((subject, index) => {
            const key = groupingAllowed || subject.metadata.isJunction ? subject.metadata.name : subject.metadata.name + "_" + index;
            if (!group[key]) {
                group[key] = [subject];
                keys.push(key);
            } else {
                group[key].push(subject);
            }
        });

        return [group, keys];
    }

}