fix: get length attribute of postgres array columns (#7239)

Change loadTables in PostgresQueryRunner to use pg_catalog to find length attribute of array columns. Previously, it relied on information_schema.columns character_maximum_length, which is null for array columns. This caused synchronize to always drop and recreate array columns.

Closes: #6990

src/driver/postgres/PostgresQueryRunner.ts

@@ -1417,12 +1417,28 @@ export class PostgresQueryRunner extends BaseQueryRunner implements QueryRunner
             return `("table_schema" = '${schema}' AND "table_name" = '${name}')`;
         }).join(" OR ");
         const tablesSql = `SELECT * FROM "information_schema"."tables" WHERE ` + tablesCondition;
+
+        /**
+         * Uses standard SQL information_schema.columns table and postgres-specific 
+         * pg_catalog.pg_attribute table to get column information.
+         * @see https://stackoverflow.com/a/19541865
+         */
         const columnsSql = `
-            SELECT
-                *,
-                pg_catalog.col_description(('"' || table_catalog || '"."' || table_schema || '"."' || table_name || '"')::regclass::oid, ordinal_position) as description,
-                ('"' || "udt_schema" || '"."' || "udt_name" || '"')::"regtype" AS "regtype"
-            FROM "information_schema"."columns"
+            SELECT columns.*,
+              pg_catalog.col_description(('"' || table_catalog || '"."' || table_schema || '"."' || table_name || '"')::regclass::oid, ordinal_position) AS description,
+              ('"' || "udt_schema" || '"."' || "udt_name" || '"')::"regtype" AS "regtype",
+              pg_catalog.format_type("col_attr"."atttypid", "col_attr"."atttypmod") AS "format_type"
+              FROM "information_schema"."columns"
+              LEFT JOIN "pg_catalog"."pg_attribute" AS "col_attr"
+              ON "col_attr"."attname" = "columns"."column_name"
+              AND "col_attr"."attrelid" = (
+                SELECT
+                  "cls"."oid" FROM "pg_catalog"."pg_class" AS "cls"
+                  LEFT JOIN "pg_catalog"."pg_namespace" AS "ns"
+                  ON "ns"."oid" = "cls"."relnamespace"
+                WHERE "cls"."relname" = "columns"."table_name"
+                AND "ns"."nspname" = "columns"."table_schema"
+              )
             WHERE
             ` + tablesCondition;
 
@@ -1595,9 +1611,17 @@ export class PostgresQueryRunner extends BaseQueryRunner implements QueryRunner
                     }
 
                     // check only columns that have length property
-                    if (this.driver.withLengthColumnTypes.indexOf(tableColumn.type as ColumnType) !== -1 && dbColumn["character_maximum_length"]) {
-                        const length = dbColumn["character_maximum_length"].toString();
+                    if (this.driver.withLengthColumnTypes.indexOf(tableColumn.type as ColumnType) !== -1) {
+                      let length;
+                      if (tableColumn.isArray) {
+                        const match = /\((\d+)\)/.exec(dbColumn["format_type"]);
+                        length = match ? match[1] : undefined;
+                      } else if (dbColumn["character_maximum_length"]) {
+                        length = dbColumn["character_maximum_length"].toString();
+                      }
+                      if (length) {
                         tableColumn.length = !this.isDefaultColumnLength(table, tableColumn, length) ? length : "";
+                      }
                     }
                     tableColumn.isNullable = dbColumn["is_nullable"] === "YES";
                     tableColumn.isPrimary = !!columnConstraints.find(constraint => constraint["constraint_type"] === "PRIMARY");

test/github-issues/6990/entity/foo.ts

@@ -0,0 +1,15 @@
+import { Column, Entity, PrimaryGeneratedColumn } from "../../../../src";
+
+@Entity()
+export class Foo {
+    @PrimaryGeneratedColumn()
+    id: number;
+
+    @Column({
+        array: true,
+        type: "varchar",
+        length: 64,
+        nullable: true,
+    })
+    varchararray: string[];    
+}

test/github-issues/6990/issue-6990.ts

@@ -0,0 +1,46 @@
+import "reflect-metadata";
+import {
+    closeTestingConnections,
+    createTestingConnections,
+    reloadTestingDatabases,
+} from "../../utils/test-utils";
+import { Connection } from "../../../src/connection/Connection";
+import { Foo } from "./entity/foo";
+import { expect } from "chai";
+
+describe("github issues > #6990 synchronize drops array columns in postgres if a length is set", () => {
+    let connections: Connection[];
+    before(
+        async () =>
+            (connections = await createTestingConnections({
+                entities: [__dirname + "/entity/*{.js,.ts}"],
+                subscribers: [__dirname + "/subscriber/*{.js,.ts}"],
+                enabledDrivers: ["postgres"],
+            }))
+    );
+    beforeEach(() => reloadTestingDatabases(connections));
+    after(() => closeTestingConnections(connections));
+
+    it("should not drop varchar array column on synchronize using postgres driver", () =>
+        Promise.all(
+            connections.map(async function (connection) {
+                const foo = new Foo();
+                foo.id = 1;
+                foo.varchararray = ["able", "baker", "charlie"];
+                await connection.manager.save(foo);
+
+                await connection.synchronize();
+
+                const loadedFoo:
+                    | Foo
+                    | undefined = await connection.manager.findOne(Foo, 1);
+
+                expect(loadedFoo).to.be.not.empty;
+                expect(loadedFoo!.varchararray).to.deep.eq([
+                    "able",
+                    "baker",
+                    "charlie",
+                ]);
+            })
+        ));
+});