diff --git a/packages/core/src/hierarchy.ts b/packages/core/src/hierarchy.ts
index 2dd2e6f416..0c47c03301 100644
--- a/packages/core/src/hierarchy.ts
+++ b/packages/core/src/hierarchy.ts
@@ -16,12 +16,10 @@
 import type { AnyAttribute, Class, Classifier, Doc, Domain, Interface, Mixin, Obj, Ref } from './classes'
 import { ClassifierKind } from './classes'
 import core from './component'
+import { _createMixinProxy, _mixinClass, _toDoc } from './proxy'
 import type { Tx, TxCreateDoc, TxMixin } from './tx'
 import { TxProcessor } from './tx'
 
-const PROXY_TARGET_KEY = '$___proxy_target'
-const PROXY_MIXIN_CLASS_KEY = '$__mixin'
-
 /**
  * @public
  */
@@ -36,22 +34,7 @@ export class Hierarchy {
     const value = this.getClass(mixin)
     const ancestor = this.getClass(value.extends as Ref<Class<Obj>>)
     const ancestorProxy = ancestor.kind === ClassifierKind.MIXIN ? this.getMixinProxyHandler(ancestor._id) : null
-    return {
-      get (target: any, property: string, receiver: any): any {
-        if (property === PROXY_TARGET_KEY) {
-          return target
-        }
-        // We need to override _class property, to return proper mixin class.
-        if (property === PROXY_MIXIN_CLASS_KEY) {
-          return mixin
-        }
-        const value = target[mixin]?.[property]
-        if (value === undefined) {
-          return ancestorProxy !== null ? ancestorProxy.get?.(target, property, receiver) : target[property]
-        }
-        return value
-      }
-    }
+    return _createMixinProxy(value, ancestorProxy)
   }
 
   private getMixinProxyHandler (mixin: Ref<Mixin<Doc>>): ProxyHandler<Doc> {
@@ -69,15 +52,11 @@ export class Hierarchy {
   }
 
   static toDoc<D extends Doc>(doc: D): D {
-    const targetDoc = (doc as any)[PROXY_TARGET_KEY]
-    if (targetDoc !== undefined) {
-      return targetDoc as D
-    }
-    return doc
+    return _toDoc(doc)
   }
 
   static mixinClass<D extends Doc, M extends D>(doc: D): Ref<Mixin<M>>|undefined {
-    return (doc as any)[PROXY_MIXIN_CLASS_KEY]
+    return _mixinClass(doc)
   }
 
   hasMixin<D extends Doc, M extends D>(doc: D, mixin: Ref<Mixin<M>>): boolean {
diff --git a/packages/core/src/proxy.ts b/packages/core/src/proxy.ts
new file mode 100644
index 0000000000..d32b1ffae5
--- /dev/null
+++ b/packages/core/src/proxy.ts
@@ -0,0 +1,45 @@
+import { Ref } from '.'
+import type { Doc, Mixin } from './classes'
+
+const PROXY_TARGET_KEY = '$___proxy_target'
+const PROXY_MIXIN_CLASS_KEY = '$__mixin'
+
+/**
+ * @internal
+ */
+export function _createMixinProxy (mixin: Mixin<Doc>, ancestorProxy: ProxyHandler<Doc> | null): ProxyHandler<Doc> {
+  return {
+    get (target: any, property: string, receiver: any): any {
+      if (property === PROXY_TARGET_KEY) {
+        return target
+      }
+      // We need to override _class property, to return proper mixin class.
+      if (property === PROXY_MIXIN_CLASS_KEY) {
+        return mixin._id
+      }
+      const value = target[mixin._id]?.[property]
+      if (value === undefined) {
+        return ancestorProxy !== null ? ancestorProxy.get?.(target, property, receiver) : target[property]
+      }
+      return value
+    }
+  }
+}
+
+/**
+ * @internal
+ */
+export function _toDoc<D extends Doc> (doc: D): D {
+  const targetDoc = (doc as any)[PROXY_TARGET_KEY]
+  if (targetDoc !== undefined) {
+    return targetDoc as D
+  }
+  return doc
+}
+
+/**
+ * @internal
+ */
+export function _mixinClass<D extends Doc, M extends D> (doc: D): Ref<Mixin<M>>|undefined {
+  return (doc as any)[PROXY_MIXIN_CLASS_KEY]
+}
diff --git a/packages/core/src/tx.ts b/packages/core/src/tx.ts
index 044d266f89..5546e51897 100644
--- a/packages/core/src/tx.ts
+++ b/packages/core/src/tx.ts
@@ -14,12 +14,12 @@
 //
 
 import type { KeysByType } from 'simplytyped'
-import type { Class, Data, Doc, Domain, Ref, Account, Space, Arr, Mixin, PropertyType, AttachedDoc, AttachedData } from './classes'
-import type { DocumentQuery, FindOptions, FindResult, Storage, WithLookup, TxResult } from './storage'
+import type { Account, Arr, AttachedData, AttachedDoc, Class, Data, Doc, Domain, Mixin, PropertyType, Ref, Space } from './classes'
 import core from './component'
-import { generateId } from './utils'
 import { _getOperator } from './operator'
-import { Hierarchy } from './hierarchy'
+import { _toDoc } from './proxy'
+import type { DocumentQuery, FindOptions, FindResult, Storage, TxResult, WithLookup } from './storage'
+import { generateId } from './utils'
 
 /**
  * @public
@@ -239,7 +239,7 @@ export abstract class TxProcessor implements WithTx {
   }
 
   static updateDoc2Doc<T extends Doc>(rawDoc: T, tx: TxUpdateDoc<T>): T {
-    const doc = Hierarchy.toDoc(rawDoc)
+    const doc = _toDoc(rawDoc)
     const ops = tx.operations as any
     for (const key in ops) {
       if (key.startsWith('$')) {
@@ -256,7 +256,7 @@ export abstract class TxProcessor implements WithTx {
 
   static updateMixin4Doc<D extends Doc, M extends D>(rawDoc: D, mixinClass: Ref<Class<M>>, operations: MixinUpdate<D, M>): D {
     const ops = operations as any
-    const doc = Hierarchy.toDoc(rawDoc)
+    const doc = _toDoc(rawDoc)
     const mixin = (doc as any)[mixinClass] ?? {}
     for (const key in ops) {
       if (key.startsWith('$')) {