Fixed – The method ‘GroupJoin’ cannot follow the method ‘SelectMany’ or is not supported while using LINQ query (Dataverse / Dynamics 365)

When using LINQ to query Dataverse, you may encounter the error "System.NotSupportedException: 'The method 'GroupJoin' cannot follow the method 'SelectMany' or is not supported." This error occurs because the GroupJoin method is not supported in the Dataverse/LINQ provider for Dynamics CRM. The issue is related to how the LINQ provider translates queries into FetchXML or SQL that Dataverse understands. To fix this error, you can break the query into multiple steps or use FetchXML or QueryExpression instead. However, using multiple steps can increase transfer and processing overhead. The better alternative for performance is to use FetchXML or QueryExpression.

Article 3m Nishant Rana's Weblog

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