added DQ over AS limitations documentation (#183)

* added DQ over AS limitations documentation

Author: mlonsk

content/common/Semantic Model/direct-query-over-as.md

@@ -0,0 +1,57 @@
+---
+uid: dq-over-as-limitations
+title: Direct Query over Analysis Services
+author: Morten Lønskov
+updated: 2025-07-14
+applies_to:
+  versions:
+    - version: 2.x
+    - version: 3.x
+  editions:
+    - edition: Desktop
+    - edition: Business
+    - edition: Enterprise
+---
+
+## Overview
+
+Tabular Editor 3 can **connect** to composite models that leverage **DirectQuery over Analysis Services (DQ‑over‑AS)**, but full modeling support is **not yet available**.  Most authoring tasks work as expected; however, operations that rely on synchronising metadata with the remote semantic model—such as *Update table schema*—are currently limited.
+
+>[!IMPORTANT]
+> Until full DQ‑over‑AS support ships, model metadata edited in Tabular Editor 3 **is not automatically kept in sync** with the source dataset. You must apply one of the work‑arounds listed below whenever columns or measures are added to the underlying Analysis Services model.
+
+## Current limitations
+
+| Feature                     | Status in TE3   | Notes                                                                                      |
+| --------------------------- | --------------- | ------------------------------------------------------------------------------------------ |
+| **Update table schema**     | ❌ Not supported | Attempting to run **Model > Update table schema** on a DQ‑over‑AS table has no effect.     |
+| **Measure synchronisation** | ❌ Not supported | Measures created in the source dataset do not appear automatically in the composite model. |
+
+## Work‑arounds
+
+### 1. Manually add missing columns
+
+1. In **TOM Explorer**, select the table that requires the new column.
+2. Choose **Add > Data Column**.
+3. In the *Properties* window, set:
+
+   * **SourceColumnName** – *exactly* match the **Name** of the column in the remote table.
+   * **SourceLineageTag** – copy the **LineageTag** value from the source column.
+4. Save and deploy the model.
+
+>[!NOTE]
+> Column names and lineage tags must match *character‑for‑character*.  Any mismatch will cause deployment errors.
+
+### 2. Use the “Import tables from remote model” C# script
+
+Daniel Otykier’s article on LinkedIn provides a [ready‑made C# automation script](https://www.linkedin.com/pulse/composite-models-tabular-editor-daniel-otykier/) that:
+
+1. Temporarily imports full copies of tables from the remote model.
+2. Lets you copy columns (and other metadata) into existing tables.
+3. Deletes the temporary tables after the copy is complete.
+
+This approach is faster when several tables require updates.
+
+### 3. One‑click macro to pull new measures
+
+[rem-bou's](https://github.com/rem-bou) GitHub repository contains an advanced macro that scans the source dataset for measures that are **missing** in the composite model and adds them automatically: [Create-Update DQ over AS model connection](https://github.com/rem-bou/TabularEditor-Scripts/blob/main/Advanced/One-Click%20Macros/Create-Update%20DQ%20over%20AS%20model%20connection.csx)

content/common/toc.md

@@ -8,6 +8,8 @@
 ### [BPA Sample Rules Expression](xref:using-bpa-sample-rules-expressions)
 ## [Semantic Model Types](Semantic Model/semantic-model-types.md)
 ### [Direct Lake on SQL](Semantic Model/direct-lake-sql-model.md)
+### [Direct Query over Analysis Services](Semantic Model/direct-query-over-as.md)
+