Updating the Patch article for explicit use of As and ThisRecord.

Author: lancedMicrosoft

powerapps-docs/maker/canvas-apps/functions/function-patch.md

@@ -67,6 +67,10 @@ Specify two or more records that you want to merge. Records are processed in the
 
 **Patch** returns the merged record and doesn't modify its arguments or records in any data sources.
 
+ 
+
+
+
 ## Syntax
 #### Modify or create a record in a data source
 **Patch**( *DataSource*, *BaseRecord*, *ChangeRecord1* [, *ChangeRecord2*, … ])
@@ -108,3 +112,137 @@ After the previous formulas have been evaluated, the data source ends with these
 | --- | --- | --- |
 | **Patch(&nbsp;{&nbsp;Name:&nbsp;"James",&nbsp;Score:&nbsp;90&nbsp;}, {&nbsp;Name:&nbsp;"Jim",&nbsp;Passed:&nbsp;true&nbsp;} )** |Merges two records outside of a data source:<br><ul><li>The values in the **Name** column of each record don't match. The result contains the value (**Jim**) in the record that's closer to the end of the argument list instead of the value (**James**) in the record that's closer to the start.</li><li>The first record contains a column (**Score**) that doesn't exist in the second record. The result contains that column with its value (**90**).</li><li>The second record contains a column (**Passed**) that doesn't exist in the first record. The result contains that column with its value (**true**). |{&nbsp;Name:&nbsp;"Jim", Score:&nbsp;90, Passed:&nbsp;true&nbsp;} |
 
+### Use of **As** or **ThisRecord**
+Avoid an ambiguous evaluation context by using the **As** or **ThisRecord** keyword. 
+
+In the example below, consider the first Lookup in the If statement. (OrderID = A[@OrderID]) is expected to compare the OrderId in the Lookup scope with the OrderId of collection A in the ForAll scope. In this case, you likely want A[@OrderId] to be resolved as a local parameter. But it is ambiguous.
+
+Power Apps currently interprets both the LHS side OrderId and RHS side A[@OrderId] as a field in the Lookup scope. Therefore, Lookup will always find the first row in [dbo].[Orders1] because the condition is always true (i.e., any row's OrderId is equal to itself.)
+
+```powerapps-dot
+ClearCollect(
+    A,
+    Filter(
+        '[dbo].[Orders1]',
+        OrderId = 8888888
+    )
+);
+ForAll(
+    A,
+    If(
+        LookUp(
+            '[dbo].[Orders1]',
+            OrderId = A[@OrderId],
+            "OK"
+        ) = "OK",
+        Patch(
+            '[dbo].[Orders1]',
+            LookUp(
+                '[dbo].[Orders1]',
+                OrderId = A[@OrderId]
+            ),
+            {
+		OrderName: "val1"
+	    }
+	),
+	Patch(
+            '[dbo].[Orders1]',
+            Defaults('[dbo].[Orders1]'),
+            {
+		OrderName: "val2"
+	    }
+	)
+    )
+)
+```
+
+#### Using **As** or **ThisRecord**
+
+Whenever possible use the **As** operator or the **ThisRecord** to disambiguate the LHS. **As** is recommended for the above scenario.
+
+When your formula uses multiple scopes with ForAll, Filter, Lookup on the same data source or table, it is possible that the scope parameters may collide with a same named field elsewhere.  Therefore, it is also recommended to use the **As** operator or **ThisRecord** to resolve the field name and avoid ambiguity.
+
+For example, we can use the **As** operator to disambiguate in the example below. 
+
+```powerapps-dot
+ClearCollect(
+    A,
+    Filter(
+        '[dbo].[Orders1]',
+        OrderId = 8888888
+    )
+);
+ForAll(
+    A,
+    If(
+        LookUp(
+            '[dbo].[Orders1]' As B,
+            B.OrderId = A[@OrderId],
+            "OK"
+        ) = "OK",
+        Patch(
+            '[dbo].[Orders1]',
+            LookUp(
+                '[dbo].[Orders1]' As C,
+                C.OrderId = A[@OrderId]
+            ),
+            {
+		OrderName: "val1"
+	    }
+	),
+	Patch(
+            '[dbo].[Orders1]',
+            Defaults('[dbo].[Orders1]'),
+            {
+		OrderName: "val2"
+	    }
+	)
+    )
+)
+```
+
+Alternatively, we can use **ThisRecord** for the same purpose.
+
+```powerapps-dot
+ClearCollect(
+    A,
+    Filter(
+        '[dbo].[Orders1]',
+        OrderId = 8888888
+    )
+);
+ForAll(
+    A,
+    If(
+        LookUp(
+            '[dbo].[Orders1]',
+            ThisRecord.OrderId = A[@OrderId],
+            "OK"
+        ) = "OK",
+        Patch(
+            '[dbo].[Orders1]',
+            LookUp(
+                '[dbo].[Orders1]',
+                ThisRecord.OrderId = A[@OrderId]
+            ),
+            {
+		OrderName: "val1"
+	    }
+	),
+	Patch(
+            '[dbo].[Orders1]',
+            Defaults('[dbo].[Orders1]'),
+            {
+		OrderName: "val2"
+	    }
+	)
+    )
+)
+```
+For detailed usage of the **As** operator and **ThisRecord**. For details, please see the **[Operators](operators.md)** article.
+
+
+
+
+
+