Updating order order of variable evaluation in Multiple create order helper (#2195)

## Why make this change?
The variables `doesSourceBodyContainAnyRelationshipField` and
`doesTargetBodyContainAnyRelationshipField` were updated after the
checks based on them were performed. Instead, they should be updated
before the checks are performed.

## What is this change?

Moved the updation of variables before the checks are performed.

## How was this tested?
NA

Author: ayush3797

src/Core/Resolvers/MultipleCreateOrderHelper.cs

@@ -220,11 +220,20 @@ private static string DetermineReferencingEntityBasedOnRequestBody(
                 if (doesSourceContainAnyAutogenRelationshipField && doesTargetContainAnyAutogenRelationshipField)
                 {
                     throw new DataApiBuilderException(
-                        message: $"Both source entity: {sourceEntityName} and target entity: {targetEntityName} contain autogenerated fields for relationship: {relationshipName} at level: {nestingLevel}",
+                        message: $"Cannot execute multiple-create because both the source entity: {sourceEntityName} and the target entity: " +
+                        $"{targetEntityName} contain autogenerated fields for relationship: {relationshipName} at level: {nestingLevel}",
                         statusCode: HttpStatusCode.BadRequest,
                         subStatusCode: DataApiBuilderException.SubStatusCodes.BadRequest);
                 }
 
+                // Determine whether the input data for source/target contain a value (could be null) for this pair of relationship fields.
+                bool doesSourceBodyContainThisRelationshipField = columnDataInSourceBody.TryGetValue(relationshipFieldInSource, out IValueNode? sourceColumnvalue);
+                bool doesTargetBodyContainThisRelationshipField = columnDataInTargetBody.TryGetValue(relationshipFieldInTarget, out IValueNode? targetColumnvalue);
+
+                // Update whether input data for source/target contains any relationship field.
+                doesSourceBodyContainAnyRelationshipField = doesSourceBodyContainAnyRelationshipField || doesSourceBodyContainThisRelationshipField;
+                doesTargetBodyContainAnyRelationshipField = doesTargetBodyContainAnyRelationshipField || doesTargetBodyContainThisRelationshipField;
+
                 // If the source entity contains a relationship field in request body which suggests we perform the insertion first in source entity,
                 // and there is an autogenerated relationship field in the target entity which suggests we perform the insertion first in target entity,
                 // we cannot determine a valid order of insertion.
@@ -247,14 +256,6 @@ private static string DetermineReferencingEntityBasedOnRequestBody(
                         subStatusCode: DataApiBuilderException.SubStatusCodes.BadRequest);
                 }
 
-                // Determine whether the input data for source/target contain a value (could be null) for this pair of relationship fields. 
-                bool doesSourceBodyContainThisRelationshipField = columnDataInSourceBody.TryGetValue(relationshipFieldInSource, out IValueNode? sourceColumnvalue);
-                bool doesTargetBodyContainThisRelationshipField = columnDataInTargetBody.TryGetValue(relationshipFieldInTarget, out IValueNode? targetColumnvalue);
-
-                // Update whether input data for source/target contains any relationship field.
-                doesSourceBodyContainAnyRelationshipField = doesSourceBodyContainAnyRelationshipField || doesSourceBodyContainThisRelationshipField;
-                doesTargetBodyContainAnyRelationshipField = doesTargetBodyContainAnyRelationshipField || doesTargetBodyContainThisRelationshipField;
-
                 // If relationship columns are present in the input for both the source and target entities,
                 // we cannot choose one entity as the referencing entity. This is because for a referencing entity,
                 // the values for all the referencing fields should be derived from the insertion in the referenced entity.