Identities and Work Item Tracking in TFS 2015

This post details the changes introduced in Team Foundation Server 2015 regarding identity fields in the Work Item Tracking (WIT) system. It explains the historical limitations of treating identities as plain strings, leading to ambiguous assignments. The post outlines the new behaviors and restrictions of identity fields, including their determination by rules and their scope. It describes the new identity picker in the web portal and its search behavior. Crucially, it details the changes in REST API responses and accepted values for identity fields, providing examples for queries and updates. It also explains the differences in how identity strings are handled in the WIT ClientOM compared to the REST API, and introduces the GetValidDisplayName helper function for correct assignment.