fix: wrong FK loaded in multi-database environment (#6828)

Fixes an edge case where the wrong foreign key 
would be loaded when multiple databases exist 
with foreign keys that have the same name.

Fixes #6168

src/driver/mysql/MysqlQueryRunner.ts

@@ -1234,7 +1234,7 @@ export class MysqlQueryRunner extends BaseQueryRunner implements QueryRunner {
                 name = database;
                 database = this.driver.database || currentDatabase;
             }
-            return `(\`kcu\`.\`TABLE_SCHEMA\` = '${database}' AND \`kcu\`.\`TABLE_NAME\` = '${name}')`;
+            return `(\`kcu\`.\`TABLE_SCHEMA\` = '${database}' AND \`kcu\`.\`TABLE_NAME\` = '${name}' AND \`rc\`.\`CONSTRAINT_SCHEMA\` = '${database}')`;
         }).join(" OR ");
         const foreignKeysSql = `SELECT \`kcu\`.\`TABLE_SCHEMA\`, \`kcu\`.\`TABLE_NAME\`, \`kcu\`.\`CONSTRAINT_NAME\`, \`kcu\`.\`COLUMN_NAME\`, \`kcu\`.\`REFERENCED_TABLE_SCHEMA\`, ` +
             `\`kcu\`.\`REFERENCED_TABLE_NAME\`, \`kcu\`.\`REFERENCED_COLUMN_NAME\`, \`rc\`.\`DELETE_RULE\` \`ON_DELETE\`, \`rc\`.\`UPDATE_RULE\` \`ON_UPDATE\` ` +

test/github-issues/6168/issue-6168.ts

@@ -0,0 +1,106 @@
+import "reflect-metadata";
+import {Connection} from "../../../src/connection/Connection";
+import {closeTestingConnections, createTestingConnections, reloadTestingDatabases} from "../../utils/test-utils";
+import {Table} from "../../../src/schema-builder/table/Table";
+import { QueryRunner } from "../../../src";
+import { expect } from "chai";
+
+const questionName = "question";
+const categoryName = "category";
+
+const createTables = async (queryRunner: QueryRunner, dbName: string) => {
+    const questionTableName = `${dbName}.${questionName}`;
+    const categoryTableName = `${dbName}.${categoryName}`;
+
+    await queryRunner.createTable(new Table({
+        name: questionTableName,
+        columns: [
+            {
+                name: "id",
+                type: "int",
+                isPrimary: true,
+                isGenerated: true,
+                generationStrategy: "increment"
+            },
+            {
+                name: "name",
+                type: "varchar",
+            }
+        ],
+    }), true);
+
+    await queryRunner.createTable(new Table({
+        name: categoryTableName,
+        columns: [
+            {
+                name: "id",
+                type: "int",
+                isPrimary: true,
+                isGenerated: true,
+                generationStrategy: "increment"
+            },
+            {
+                name: "questionId",
+                type: "int",
+            }
+        ],
+        foreignKeys: [
+            {
+                columnNames: ["questionId"],
+                referencedTableName: questionTableName,
+                referencedColumnNames: ["id"],
+                name: "FK_CATEGORY_QUESTION"
+            }
+        ]
+    }), true);
+};
+
+describe("github issues > #6168 fix multiple foreign keys with the same name in a mysql multi-tenanted DB", () => {
+
+    let connections: Connection[];
+    before(async () => {
+        connections = await createTestingConnections({
+            entities: [__dirname + "/entity/*{.js,.ts}"],
+            enabledDrivers: ["mysql"],
+            schemaCreate: false,
+            dropSchema: false,
+        });
+
+        await reloadTestingDatabases(connections);
+
+        for (const connection of connections) {
+            const queryRunner = connection.createQueryRunner();
+            await createTables(queryRunner, String(connection.driver.database));
+            await queryRunner.createDatabase("test2", true);
+            await createTables(queryRunner, "test2");
+            await queryRunner.release();
+        };
+    });
+
+    after(async () => {
+        for (const connection of connections) {
+            const queryRunner = connection.createQueryRunner();
+            await queryRunner.dropDatabase("test2");
+            await queryRunner.release();
+        };
+
+        await closeTestingConnections(connections);
+    });
+
+    it("should only have one foreign key column", () => Promise.all(connections.map(async connection => {
+        const queryRunner = connection.createQueryRunner();
+        const tables = await queryRunner.getTables([questionName, categoryName]);
+
+        const questionTable = tables.find(table => table.name === questionName) as Table;
+        const categoryTable = tables.find(table => table.name === categoryName) as Table;
+
+        queryRunner.release();
+
+        expect(categoryTable.foreignKeys.length).to.eq(1);
+        expect(categoryTable.foreignKeys[0].name).to.eq("FK_CATEGORY_QUESTION");
+        expect(categoryTable.foreignKeys[0].columnNames.length).to.eq(1);  // before the fix this was 2, one for each schema 
+        expect(categoryTable.foreignKeys[0].columnNames[0]).to.eq("questionId");
+
+        expect(questionTable.foreignKeys.length).to.eq(0);
+    })));
+});