fix(m-n-relation): catch invalid m-n-relation

* check if second many part is available
* invalid relation
```prisma
model User {
    id Int @id @default(autoincrement())
    receivedPosts Post[] @relation("userReceivesPosts")
  }
  model Post {
    id Int @id @default(autoincrement())
    receivedBy User[] @relation("userReceivesPosts", references: [id])
  }
```
* add new test for invalid m-n-relation
* add rename m-n-relation test

Author: marcjulian

__tests__/dbml.test.ts

@@ -3,6 +3,8 @@ import {
   datamodelDbmlComments,
   datamodelDbmlDefaults,
   datamodelDbmlManyToMany,
+  datamodelDbmlManyToManyInvalid,
+  datamodelDbmlManyToManyRenameRelation,
   datamodelDbmlManyToManySelfRelation,
   datamodelDbmlRelations,
 } from './fixtures/dbml.datamodel';
@@ -235,4 +237,68 @@ Table Followers {
 
     expect(dbml).toEqual(expectedDbml);
   });
+
+  test('generating dbml schema with invalid many-to-many', async () => {
+    const dmmf = await generateDMMF(datamodelDbmlManyToManyInvalid);
+
+    const expectedDbml = `${autoGeneratedComment}
+
+Table User {
+  id Int [pk, increment]
+  receivedPosts Post [not null]
+}
+
+Table Post {
+  id Int [pk, increment]
+  receivedBy User [not null]
+}`;
+
+    const dbml = generateDBMLSchema(dmmf);
+
+    expect(dbml).toEqual(expectedDbml);
+  });
+  test('generating dbml schema with invalid many-to-many', async () => {
+    const dmmf = await generateDMMF(datamodelDbmlManyToManyInvalid);
+
+    const expectedDbml = `${autoGeneratedComment}
+
+Table User {
+  id Int [pk, increment]
+  receivedPosts Post [not null]
+}
+
+Table Post {
+  id Int [pk, increment]
+  receivedBy User [not null]
+}`;
+
+    const dbml = generateDBMLSchema(dmmf);
+
+    expect(dbml).toEqual(expectedDbml);
+  });
+  
+  test('generating dbml schema with rename many-to-many', async () => {
+    const dmmf = await generateDMMF(datamodelDbmlManyToManyRenameRelation);
+
+    const expectedDbml = `${autoGeneratedComment}
+
+Table User {
+  id Int [pk, increment]
+  receivedPosts Post [not null]
+}
+
+Table Post {
+  id Int [pk, increment]
+  receivedBy User [not null]
+}
+
+Table userReceivesPosts {
+  receivedpostsId Int [ref: > Post.id]
+  receivedbyId Int [ref: > User.id]
+}`;
+
+    const dbml = generateDBMLSchema(dmmf);
+
+    expect(dbml).toEqual(expectedDbml);
+  });
 });

__tests__/fixtures/dbml.datamodel.ts

@@ -109,3 +109,25 @@ export const datamodelDbmlManyToManySelfRelation = /* Prisma */ `
     following User[] @relation("Followers")
   }
 `;
+
+export const datamodelDbmlManyToManyInvalid = /* Prisma */ `
+  model User {
+    id Int @id @default(autoincrement())
+    receivedPosts Post[] @relation("userReceivesPosts")
+  }
+  model Post {
+    id Int @id @default(autoincrement())
+    receivedBy User[] @relation("userReceivesPosts", references: [id])
+  }
+`;
+
+export const datamodelDbmlManyToManyRenameRelation = /* Prisma */ `
+  model User {
+    id Int @id @default(autoincrement())
+    receivedPosts Post[] @relation("userReceivesPosts")
+  }
+  model Post {
+    id Int @id @default(autoincrement())
+    receivedBy User[] @relation("userReceivesPosts")
+  }
+`;

src/generator/many-to-many-tables.ts

@@ -5,7 +5,6 @@ export function generateManyToManyTables(models: DMMF.Model[]): string[] {
   if (manyToManyFields.length === 0) {
     return [];
   }
-
   return generateTables(manyToManyFields, models);
 }
 
@@ -23,6 +22,10 @@ function generateTables(
     (field) => field.relationName === manyFirst.relationName
   )!;
 
+  if (!manySecond) {
+    return manyToManyTables;
+  }
+
   manyToManyTables.push(
     `Table ${manyFirst?.relationName} {\n` +
       `${generateJoinFields([manyFirst, manySecond], models)}` +