How to retrieve from many-to-many entity.

If you need to retrieve something from many-to-many relationship entity, and there is no such entity in CRM, then you should use the FetchXml, instead of Query.

// Base bodel of FetchXml for get relationship entity
string fetchXML =
"<fetch distinct='false' mapping='logical'>" +
"<entity name='" + relationshipName + "'><filter type='and'>" +
"<condition attribute='" + relatedEntityName + "id' operator='eq' value='" + relatedId + "' />" +
"<condition attribute='" + typeEntityName + "id' operator='eq' value='" + profileId + "' />" +
"</filter></entity>" + "</fetch>";

For example, next code snippet is checking a count of relations between the Account entity and New_Industry entity, wich relationship is many-to-many. To achieve this, I need to check the relationship entity - New_industry_account, wich is contains all of relation of our two entities.

ICrmService crmService = context.CreateCrmService(true);

// check for relation
#region FetchXML
string fetchXML =
"<fetch distinct='false' mapping='logical'>" +
"<entity name='new_industry_account'><filter type='and'>" +
"<condition attribute='accountid' operator='eq' value='" + accountid.ToString() + "' />" +
"</filter></entity></fetch>";
#endregion

string fetchresult = crmService.Fetch(fetchXML);
XmlDocument xmldoc = new XmlDocument();
xmldoc.LoadXml(fetchresult);
XmlNodeList xnodlist = xmldoc.SelectNodes("resultset/result");
if (xnodlist.Count > 0) { return; }