feat: add support for defining hasOne with FK (#10441)

packages/core/types/src/dml/index.ts

@@ -51,6 +51,7 @@ export type KnownDataTypes =
  */
 export type RelationshipTypes =
   | "hasOne"
+  | "hasOneWithFK"
   | "hasMany"
   | "belongsTo"
   | "manyToMany"
@@ -111,7 +112,7 @@ export type RelationshipMetadata = {
   name: string
   type: RelationshipTypes
   entity: unknown
-  nullable: boolean
+  nullable?: boolean
   mappedBy?: string
   searchable: boolean
   options: Record<string, any>
@@ -142,9 +143,9 @@ export interface EntityConstructor<Props> extends Function {
  * "belongsTo" relation meaning "hasOne" and "ManyToOne"
  */
 export type InferForeignKeys<Schema extends DMLSchema> = {
-  [K in keyof Schema as Schema[K] extends { type: "belongsTo" }
+  [K in keyof Schema as Schema[K] extends { $foreignKey: true }
     ? `${K & string}_id`
-    : never]: Schema[K] extends { type: "belongsTo" }
+    : never]: Schema[K] extends { $foreignKey: true }
     ? null extends Schema[K]["$dataType"]
       ? string | null
       : string
@@ -191,7 +192,7 @@ export type InferSchemaFields<Schema extends DMLSchema> = Prettify<
     [K in keyof Schema]: Schema[K] extends RelationshipType<any>
       ? Schema[K]["type"] extends "belongsTo"
         ? InferBelongsToFields<Schema[K]["$dataType"]>
-        : Schema[K]["type"] extends "hasOne"
+        : Schema[K]["type"] extends "hasOne" | "hasOneWithFK"
         ? InferHasOneFields<Schema[K]["$dataType"]>
         : Schema[K]["type"] extends "hasMany"
         ? InferHasManyFields<Schema[K]["$dataType"]>

packages/core/utils/src/dml/__tests__/entity-builder.spec.ts

@@ -2887,6 +2887,690 @@ describe("Entity builder", () => {
     })
   })
 
+  describe("Entity builder | hasOneWithFK", () => {
+    test("define hasOne relationship with FK enabled", () => {
+      const email = model.define("email", {
+        email: model.text(),
+        isVerified: model.boolean(),
+      })
+
+      const user = model.define("user", {
+        id: model.number(),
+        username: model.text(),
+        email: model.hasOne(() => email, {
+          foreignKey: true,
+        }),
+      })
+
+      const User = toMikroORMEntity(user)
+
+      expectTypeOf(new User()).toEqualTypeOf<{
+        id: number
+        username: string
+        email_id: string
+        created_at: Date
+        updated_at: Date
+        deleted_at: Date | null
+        email: {
+          email: string
+          isVerified: boolean
+          created_at: Date
+          updated_at: Date
+          deleted_at: Date | null
+        }
+      }>()
+
+      const metaData = MetadataStorage.getMetadataFromDecorator(User)
+      expect(metaData.className).toEqual("User")
+      expect(metaData.path).toEqual("User")
+      expect(metaData.properties).toEqual({
+        id: {
+          reference: "scalar",
+          type: "number",
+          columnType: "integer",
+          name: "id",
+          fieldName: "id",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        username: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "username",
+          fieldName: "username",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        email: {
+          reference: "1:1",
+          name: "email",
+          entity: "Email",
+          nullable: false,
+        },
+        email_id: {
+          columnType: "text",
+          type: "string",
+          reference: "scalar",
+          name: "email_id",
+          nullable: false,
+          persist: true,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+    })
+
+    test("mark hasOne with FK enabled relationship as nullable", () => {
+      const email = model.define("email", {
+        email: model.text(),
+        isVerified: model.boolean(),
+      })
+
+      const user = model.define("user", {
+        id: model.number(),
+        username: model.text(),
+        emails: model
+          .hasOne(() => email, {
+            foreignKey: true,
+          })
+          .nullable(),
+      })
+
+      const User = toMikroORMEntity(user)
+
+      expectTypeOf(new User().emails_id).toEqualTypeOf<string | null>()
+      expectTypeOf(new User()).toMatchTypeOf<{
+        id: number
+        username: string
+        deleted_at: Date | null
+        emails_id: string | null
+        emails: {
+          email: string
+          isVerified: boolean
+          deleted_at: Date | null
+        } | null
+      }>()
+
+      const metaData = MetadataStorage.getMetadataFromDecorator(User)
+      expect(metaData.className).toEqual("User")
+      expect(metaData.path).toEqual("User")
+      expect(metaData.properties).toEqual({
+        id: {
+          reference: "scalar",
+          type: "number",
+          columnType: "integer",
+          name: "id",
+          fieldName: "id",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        username: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "username",
+          fieldName: "username",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        emails: {
+          reference: "1:1",
+          name: "emails",
+          entity: "Email",
+          nullable: true,
+        },
+        emails_id: {
+          columnType: "text",
+          type: "string",
+          reference: "scalar",
+          name: "emails_id",
+          nullable: true,
+          persist: true,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+    })
+
+    test("define custom mappedBy key for relationship", () => {
+      const email = model.define("email", {
+        email: model.text(),
+        isVerified: model.boolean(),
+      })
+
+      const user = model.define("user", {
+        id: model.number(),
+        username: model.text(),
+        email: model.hasOne(() => email, {
+          mappedBy: "owner",
+          foreignKey: true,
+        }),
+      })
+
+      const User = toMikroORMEntity(user)
+      expectTypeOf(new User().email_id).toEqualTypeOf<string>()
+      expectTypeOf(new User()).toMatchTypeOf<{
+        id: number
+        username: string
+        email: { email: string; isVerified: boolean }
+      }>()
+
+      const metaData = MetadataStorage.getMetadataFromDecorator(User)
+      expect(metaData.className).toEqual("User")
+      expect(metaData.path).toEqual("User")
+      expect(metaData.properties).toEqual({
+        id: {
+          reference: "scalar",
+          type: "number",
+          columnType: "integer",
+          name: "id",
+          fieldName: "id",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        username: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "username",
+          fieldName: "username",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        email: {
+          reference: "1:1",
+          name: "email",
+          entity: "Email",
+          nullable: false,
+          mappedBy: "owner",
+        },
+        email_id: {
+          columnType: "text",
+          type: "string",
+          reference: "scalar",
+          name: "email_id",
+          nullable: false,
+          persist: true,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+    })
+
+    test("define delete cascades for the entity", () => {
+      const email = model.define("email", {
+        email: model.text(),
+        isVerified: model.boolean(),
+      })
+
+      const user = model
+        .define("user", {
+          id: model.number(),
+          username: model.text(),
+          email: model.hasOne(() => email, {
+            foreignKey: true,
+          }),
+        })
+        .cascades({
+          delete: ["email"],
+        })
+
+      const User = toMikroORMEntity(user)
+      expectTypeOf(new User().email_id).toEqualTypeOf<string>()
+      expectTypeOf(new User()).toMatchTypeOf<{
+        id: number
+        username: string
+        email: { email: string; isVerified: boolean }
+      }>()
+
+      const metaData = MetadataStorage.getMetadataFromDecorator(User)
+      expect(metaData.className).toEqual("User")
+      expect(metaData.path).toEqual("User")
+      expect(metaData.properties).toEqual({
+        id: {
+          reference: "scalar",
+          type: "number",
+          columnType: "integer",
+          name: "id",
+          fieldName: "id",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        username: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "username",
+          fieldName: "username",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        email: {
+          reference: "1:1",
+          name: "email",
+          entity: "Email",
+          nullable: false,
+          cascade: ["persist", "soft-remove"],
+        },
+        email_id: {
+          columnType: "text",
+          type: "string",
+          reference: "scalar",
+          name: "email_id",
+          nullable: false,
+          persist: true,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+
+      const Email = toMikroORMEntity(email)
+      const emailMetaData = MetadataStorage.getMetadataFromDecorator(Email)
+      expect(emailMetaData.className).toEqual("Email")
+      expect(emailMetaData.path).toEqual("Email")
+      expect(emailMetaData.properties).toEqual({
+        email: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "email",
+          fieldName: "email",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        isVerified: {
+          reference: "scalar",
+          type: "boolean",
+          columnType: "boolean",
+          name: "isVerified",
+          fieldName: "isVerified",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+    })
+
+    test("define delete cascades with belongsTo on the other end", () => {
+      const email = model.define("email", {
+        email: model.text(),
+        isVerified: model.boolean(),
+        user: model.belongsTo(() => user),
+      })
+
+      const user = model
+        .define("user", {
+          id: model.number(),
+          username: model.text(),
+          email: model.hasOne(() => email, {
+            foreignKey: true,
+          }),
+        })
+        .cascades({
+          delete: ["email"],
+        })
+
+      const User = toMikroORMEntity(user)
+      expectTypeOf(new User().email_id).toEqualTypeOf<string>()
+      expectTypeOf(new User()).toMatchTypeOf<{
+        id: number
+        username: string
+        email: {
+          email: string
+          isVerified: boolean
+          user: {
+            id: number
+            username: string
+          }
+        }
+      }>()
+
+      const metaData = MetadataStorage.getMetadataFromDecorator(User)
+      expect(metaData.className).toEqual("User")
+      expect(metaData.path).toEqual("User")
+      expect(metaData.properties).toEqual({
+        id: {
+          reference: "scalar",
+          type: "number",
+          columnType: "integer",
+          name: "id",
+          fieldName: "id",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        username: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "username",
+          fieldName: "username",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        email: {
+          reference: "1:1",
+          name: "email",
+          entity: "Email",
+          nullable: false,
+          cascade: ["persist", "soft-remove"],
+        },
+        email_id: {
+          columnType: "text",
+          type: "string",
+          reference: "scalar",
+          name: "email_id",
+          nullable: false,
+          persist: true,
+          getter: false,
+          setter: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+
+      const Email = toMikroORMEntity(email)
+      const emailMetaData = MetadataStorage.getMetadataFromDecorator(Email)
+      expect(emailMetaData.className).toEqual("Email")
+      expect(emailMetaData.path).toEqual("Email")
+      expect(emailMetaData.properties).toEqual({
+        email: {
+          reference: "scalar",
+          type: "string",
+          columnType: "text",
+          name: "email",
+          fieldName: "email",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        isVerified: {
+          reference: "scalar",
+          type: "boolean",
+          columnType: "boolean",
+          name: "isVerified",
+          fieldName: "isVerified",
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        user: {
+          entity: "User",
+          mappedBy: "email",
+          name: "user",
+          nullable: false,
+          onDelete: "cascade",
+          owner: true,
+          reference: "1:1",
+        },
+        user_id: {
+          columnType: "text",
+          getter: false,
+          name: "user_id",
+          nullable: false,
+          reference: "scalar",
+          setter: false,
+          type: "string",
+          persist: false,
+        },
+        created_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "created_at",
+          fieldName: "created_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        updated_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "updated_at",
+          fieldName: "updated_at",
+          defaultRaw: "now()",
+          onCreate: expect.any(Function),
+          onUpdate: expect.any(Function),
+          nullable: false,
+          getter: false,
+          setter: false,
+        },
+        deleted_at: {
+          reference: "scalar",
+          type: "date",
+          columnType: "timestamptz",
+          name: "deleted_at",
+          fieldName: "deleted_at",
+          nullable: true,
+          getter: false,
+          setter: false,
+        },
+      })
+    })
+  })
+
   describe("Entity builder | indexes", () => {
     test("should define indexes for an entity", () => {
       const group = model.define("group", {

packages/core/utils/src/dml/__tests__/has-one-relationship.spec.ts

@@ -1,6 +1,7 @@
 import { expectTypeOf } from "expect-type"
 import { TextProperty } from "../properties/text"
 import { HasOne } from "../relations/has-one"
+import { HasOneWithForeignKey } from "../relations/has-one-fk"
 
 describe("HasOne relationship", () => {
   test("define hasOne relationship", () => {
@@ -57,4 +58,23 @@ describe("HasOne relationship", () => {
 
     expect(HasOne.isHasOne(relationship)).toEqual(false)
   })
+
+  test("enable foreign keys for has one relationship", () => {
+    const user = {
+      username: new TextProperty(),
+    }
+
+    const entityRef = () => user
+    const relationship = new HasOneWithForeignKey(entityRef, {})
+
+    expectTypeOf(relationship["$dataType"]).toEqualTypeOf<() => typeof user>()
+    expect(relationship.parse("user")).toEqual({
+      name: "user",
+      type: "hasOneWithFK",
+      nullable: false,
+      options: {},
+      searchable: false,
+      entity: entityRef,
+    })
+  })
 })

packages/core/utils/src/dml/entity-builder.ts

@@ -25,6 +25,7 @@ import { BelongsTo } from "./relations/belongs-to"
 import { HasMany } from "./relations/has-many"
 import { HasOne } from "./relations/has-one"
 import { ManyToMany } from "./relations/many-to-many"
+import { HasOneWithForeignKey } from "./relations/has-one-fk"
 
 /**
  * The implicit properties added by EntityBuilder in every schema
@@ -345,7 +346,27 @@ export class EntityBuilder {
    *
    * @customNamespace Relationship Methods
    */
-  hasOne<T>(entityBuilder: T, options?: RelationshipOptions) {
+  hasOne<T>(
+    entityBuilder: T,
+    options: RelationshipOptions & {
+      foreignKey: true
+    }
+  ): HasOneWithForeignKey<T>
+  hasOne<T>(
+    entityBuilder: T,
+    options?: RelationshipOptions & {
+      foreignKey?: false
+    }
+  ): HasOne<T>
+  hasOne<T>(
+    entityBuilder: T,
+    options?: RelationshipOptions & {
+      foreignKey?: boolean
+    }
+  ): HasOneWithForeignKey<T> | HasOne<T> {
+    if (options?.foreignKey) {
+      return new HasOneWithForeignKey<T>(entityBuilder, options || {})
+    }
     return new HasOne<T>(entityBuilder, options || {})
   }
 

packages/core/utils/src/dml/entity.ts

@@ -139,7 +139,7 @@ export class DmlEntity<
    */
   cascades(
     options: EntityCascades<
-      ExtractEntityRelations<Schema, "hasOne" | "hasMany">
+      ExtractEntityRelations<Schema, "hasOne" | "hasOneWithFK" | "hasMany">
     >
   ) {
     const childToParentCascades = options.delete?.filter((relationship) => {

packages/core/utils/src/dml/helpers/entity-builder/define-relationship.ts

@@ -22,6 +22,7 @@ import { parseEntityName } from "./parse-entity-name"
 import { camelToSnakeCase, pluralize } from "../../../common"
 import { applyEntityIndexes } from "../mikro-orm/apply-indexes"
 import { ManyToMany as DmlManyToMany } from "../../relations/many-to-many"
+import { HasOneWithForeignKey } from "../../relations/has-one-fk"
 
 type Context = {
   MANY_TO_MANY_TRACKED_RELATIONS: Record<string, boolean>
@@ -150,6 +151,43 @@ export function defineHasOneRelationship(
   })(MikroORMEntity.prototype, relationship.name)
 }
 
+/**
+ * Defines has one relationship with Foreign key on the MikroORM
+ * entity
+ */
+export function defineHasOneWithFKRelationship(
+  MikroORMEntity: EntityConstructor<any>,
+  relationship: RelationshipMetadata,
+  { relatedModelName }: { relatedModelName: string },
+  cascades: EntityCascades<string[]>
+) {
+  const foreignKeyName = camelToSnakeCase(`${relationship.name}Id`)
+  const shouldRemoveRelated = !!cascades.delete?.includes(relationship.name)
+  let mappedBy: string | undefined
+
+  if ("mappedBy" in relationship) {
+    mappedBy = relationship.mappedBy
+  } else {
+    mappedBy = camelToSnakeCase(MikroORMEntity.name)
+  }
+
+  OneToOne({
+    entity: relatedModelName,
+    nullable: relationship.nullable,
+    ...(mappedBy ? { mappedBy } : {}),
+    cascade: shouldRemoveRelated
+      ? (["persist", "soft-remove"] as any)
+      : undefined,
+  } as any)(MikroORMEntity.prototype, relationship.name)
+
+  Property({
+    type: "string",
+    columnType: "text",
+    nullable: relationship.nullable,
+    persist: true,
+  })(MikroORMEntity.prototype, foreignKeyName)
+}
+
 /**
  * Defines has many relationship on the Mikro ORM entity
  */
@@ -225,7 +263,10 @@ export function defineBelongsToRelationship(
        * to associate a relation (through the relation or the foreign key) we need to handle it
        * specifically
        */
-      if (HasOne.isHasOne(otherSideRelation)) {
+      if (
+        HasOne.isHasOne(otherSideRelation) ||
+        HasOneWithForeignKey.isHasOneWithForeignKey(otherSideRelation)
+      ) {
         const relationMeta = this.__meta.relations.find(
           (relation) => relation.name === relationship.name
         ).targetMeta
@@ -317,7 +358,10 @@ export function defineBelongsToRelationship(
   /**
    * Otherside is a has one. Hence we should defined a OneToOne
    */
-  if (HasOne.isHasOne(otherSideRelation)) {
+  if (
+    HasOne.isHasOne(otherSideRelation) ||
+    HasOneWithForeignKey.isHasOneWithForeignKey(otherSideRelation)
+  ) {
     const foreignKeyName = camelToSnakeCase(`${relationship.name}Id`)
 
     OneToOne({
@@ -600,6 +644,14 @@ export function defineRelationship(
         cascades
       )
       break
+    case "hasOneWithFK":
+      defineHasOneWithFKRelationship(
+        MikroORMEntity,
+        relationship,
+        relatedEntityInfo,
+        cascades
+      )
+      break
     case "hasMany":
       defineHasManyRelationship(
         MikroORMEntity,

packages/core/utils/src/dml/relations/base.ts

@@ -56,8 +56,6 @@ export abstract class BaseRelationship<T> implements RelationshipType<T> {
    * })
    *
    * export default Product
-   *
-   * @customNamespace Property Configuration Methods
    */
   searchable() {
     this.#searchable = true

packages/core/utils/src/dml/relations/belongs-to.ts

@@ -3,6 +3,7 @@ import { RelationNullableModifier } from "./nullable"
 
 export class BelongsTo<T> extends BaseRelationship<T> {
   type = "belongsTo" as const
+  declare $foreignKey: true
 
   static isBelongsTo<T>(relationship: any): relationship is BelongsTo<T> {
     return relationship?.type === "belongsTo"
@@ -12,6 +13,6 @@ export class BelongsTo<T> extends BaseRelationship<T> {
    * Apply nullable modifier on the schema
    */
   nullable() {
-    return new RelationNullableModifier<T, BelongsTo<T>>(this)
+    return new RelationNullableModifier<T, BelongsTo<T>, true>(this)
   }
 }

packages/core/utils/src/dml/relations/has-one-fk.ts

@@ -0,0 +1,30 @@
+import { BaseRelationship } from "./base"
+import { RelationNullableModifier } from "./nullable"
+
+/**
+ * HasOne relationship defines a relationship between two entities
+ * where the owner of the relationship has exactly one instance
+ * of the related entity.
+ *
+ * For example: A user HasOne profile
+ *
+ * You may use the "BelongsTo" relationship to define the inverse
+ * of the "HasOne" relationship
+ */
+export class HasOneWithForeignKey<T> extends BaseRelationship<T> {
+  type = "hasOneWithFK" as const
+  declare $foreignKey: true
+
+  static isHasOneWithForeignKey<T>(
+    relationship: any
+  ): relationship is HasOneWithForeignKey<T> {
+    return relationship?.type === "hasOneWithFK"
+  }
+
+  /**
+   * Apply nullable modifier on the schema
+   */
+  nullable() {
+    return new RelationNullableModifier<T, HasOneWithForeignKey<T>, true>(this)
+  }
+}

packages/core/utils/src/dml/relations/has-one.ts

@@ -22,6 +22,6 @@ export class HasOne<T> extends BaseRelationship<T> {
    * Apply nullable modifier on the schema
    */
   nullable() {
-    return new RelationNullableModifier<T, HasOne<T>>(this)
+    return new RelationNullableModifier<T, HasOne<T>, false>(this)
   }
 }

packages/core/utils/src/dml/relations/nullable.ts

@@ -6,15 +6,18 @@ const IsNullableModifier = Symbol.for("isNullableModifier")
 /**
  * Nullable modifier marks a schema node as nullable
  */
-export class RelationNullableModifier<T, Relation extends RelationshipType<T>>
+export class RelationNullableModifier<
-  implements RelationshipType<T | null>
+  T,
+  Relation extends RelationshipType<T>,
+  ForeignKey extends boolean
+> implements RelationshipType<T | null>
 {
   [IsNullableModifier]: true = true;
   [IsRelationship]: true = true
 
   static isNullableModifier<T>(
     modifier: any
-  ): modifier is RelationNullableModifier<T, any> {
+  ): modifier is RelationNullableModifier<T, any, any> {
     return !!modifier?.[IsNullableModifier]
   }
 
@@ -25,6 +28,7 @@ export class RelationNullableModifier<T, Relation extends RelationshipType<T>>
    * of the schema property
    */
   declare $dataType: T | null
+  declare $foreignKey: ForeignKey
 
   /**
    * The parent schema on which the nullable modifier is