fix(mysql): mark FK columns as unsigned for mixed composite PKs

Closes #2844

packages/core/src/metadata/MetadataDiscovery.ts

@@ -998,7 +998,8 @@ export class MetadataDiscovery {
 
       meta2.primaryKeys.forEach(primaryKey => {
         const pk = meta2.properties[primaryKey];
-        prop.unsigned = this.platform.supportsUnsigned() && this.isNumericProperty(pk);
+        // if at least one of the target columns is unsigned, we need to mark the property as unsigned
+        prop.unsigned ||= this.platform.supportsUnsigned() && this.isNumericProperty(pk);
       });
 
       return;

tests/features/schema-generator/GH2844.test.ts

@@ -0,0 +1,68 @@
+import { Entity, Index, ManyToOne, MikroORM, OneToOne, PrimaryKey, Property } from '@mikro-orm/core';
+
+@Entity()
+export class UserAction {
+
+  @PrimaryKey()
+  idUserAction!: string;
+
+  @Property()
+  name!: string;
+
+}
+
+@Entity()
+@Index({ properties: ['id', 'userAction'] })
+export class Step {
+
+  @PrimaryKey()
+  id!: number;
+
+  @ManyToOne({ primary: true, onDelete: 'cascade' })
+  userAction!: UserAction;
+
+}
+
+@Entity()
+export class Component {
+
+  @PrimaryKey()
+  idComponent!: string;
+
+  @ManyToOne({ onDelete: 'cascade' })
+  step!: Step;
+
+  @OneToOne({
+    nullable: true,
+    fieldName: 'resultComponentId',
+    unique: false,
+    entity: () => Component,
+  })
+  resultComponent?: Component;
+
+}
+
+describe('complex FKs in mariadb (GH 2844)', () => {
+
+  let orm: MikroORM;
+
+  beforeAll(async () => {
+    orm = await MikroORM.init({
+      entities: [Component, Step, UserAction],
+      dbName: `mikro_orm_test_gh_2844`,
+      type: 'mariadb',
+      port: 3309,
+    });
+    await orm.getSchemaGenerator().ensureDatabase();
+    await orm.getSchemaGenerator().dropSchema();
+  });
+
+  afterAll(() => orm.close(true));
+
+  test('schema generator adds the m:1 columns and FK properly', async () => {
+    const sql = await orm.getSchemaGenerator().getCreateSchemaSQL();
+    expect(sql).toMatchSnapshot();
+    await orm.getSchemaGenerator().execute(sql);
+  });
+
+});