diff --git a/app/__test__/data/specs/Repository.spec.ts b/app/__test__/data/specs/Repository.spec.ts
index d9b2dc2..efb987d 100644
--- a/app/__test__/data/specs/Repository.spec.ts
+++ b/app/__test__/data/specs/Repository.spec.ts
@@ -124,6 +124,81 @@ describe("[Repository]", async () => {
             .then((r) => [r.count, r.total]),
       ).resolves.toEqual([undefined, undefined]);
    });
+
+   test("auto join", async () => {
+      const schema = $em(
+         {
+            posts: $entity("posts", {
+               title: $text(),
+               content: $text(),
+            }),
+            comments: $entity("comments", {
+               content: $text(),
+            }),
+            another: $entity("another", {
+               title: $text(),
+            }),
+         },
+         ({ relation }, { posts, comments }) => {
+            relation(comments).manyToOne(posts);
+         },
+      );
+      const em = schema.proto.withConnection(getDummyConnection().dummyConnection);
+      await em.schema().sync({ force: true });
+
+      await em.mutator("posts").insertOne({ title: "post1", content: "content1" });
+      await em
+         .mutator("comments")
+         .insertMany([{ content: "comment1", posts_id: 1 }, { content: "comment2" }] as any);
+
+      const res = await em.repo("comments").findMany({
+         where: {
+            "posts.title": "post1",
+         },
+      });
+      expect(res.data as any).toEqual([
+         {
+            id: 1,
+            content: "comment1",
+            posts_id: 1,
+         },
+      ]);
+
+      {
+         // manual join should still work
+         const res = await em.repo("comments").findMany({
+            join: ["posts"],
+            where: {
+               "posts.title": "post1",
+            },
+         });
+         expect(res.data as any).toEqual([
+            {
+               id: 1,
+               content: "comment1",
+               posts_id: 1,
+            },
+         ]);
+      }
+
+      // inexistent should be detected and thrown
+      expect(
+         em.repo("comments").findMany({
+            where: {
+               "random.title": "post1",
+            },
+         }),
+      ).rejects.toThrow(/Invalid where field/);
+
+      // existing alias, but not a relation should throw
+      expect(
+         em.repo("comments").findMany({
+            where: {
+               "another.title": "post1",
+            },
+         }),
+      ).rejects.toThrow(/Invalid where field/);
+   });
 });
 
 describe("[data] Repository (Events)", async () => {
diff --git a/app/src/data/entities/query/Repository.ts b/app/src/data/entities/query/Repository.ts
index 3d8f432..218f25e 100644
--- a/app/src/data/entities/query/Repository.ts
+++ b/app/src/data/entities/query/Repository.ts
@@ -103,6 +103,7 @@ export class Repository<TBD extends object = DefaultDB, TB extends keyof TBD = a
          validated.with = options.with;
       }
 
+      // add explicit joins. Implicit joins are added in `where` builder
       if (options.join && options.join.length > 0) {
          for (const entry of options.join) {
             const related = this.em.relationOf(entity.name, entry);
@@ -127,12 +128,28 @@ export class Repository<TBD extends object = DefaultDB, TB extends keyof TBD = a
          const invalid = WhereBuilder.getPropertyNames(options.where).filter((field) => {
             if (field.includes(".")) {
                const [alias, prop] = field.split(".") as [string, string];
-               if (!aliases.includes(alias)) {
+               // check aliases first (added joins)
+               if (aliases.includes(alias)) {
+                  this.checkIndex(alias, prop, "where");
+                  return !this.em.entity(alias).getField(prop);
+               }
+               // check if alias (entity) exists
+               if (!this.em.hasEntity(alias)) {
                   return true;
                }
+               // check related fields for auto join
+               const related = this.em.relationOf(entity.name, alias);
+               if (related) {
+                  const other = related.other(entity);
+                  if (other.entity.getField(prop)) {
+                     // if related field is found, add join to validated options
+                     validated.join?.push(alias);
+                     this.checkIndex(alias, prop, "where");
+                     return false;
+                  }
+               }
 
-               this.checkIndex(alias, prop, "where");
-               return !this.em.entity(alias).getField(prop);
+               return true;
             }
 
             this.checkIndex(entity.name, field, "where");
diff --git a/app/src/data/prototype/index.ts b/app/src/data/prototype/index.ts
index 43df6a1..0741f95 100644
--- a/app/src/data/prototype/index.ts
+++ b/app/src/data/prototype/index.ts
@@ -289,7 +289,7 @@ class EntityManagerPrototype<Entities extends Record<string, Entity>> extends En
       super(Object.values(__entities), new DummyConnection(), relations, indices);
    }
 
-   withConnection(connection: Connection): EntityManager<Schema<Entities>> {
+   withConnection(connection: Connection): EntityManager<Schemas<Entities>> {
       return new EntityManager(this.entities, connection, this.relations.all, this.indices);
    }
 }