Sample code (C#) for Multi-Table Lookup / Polymorphic Lookup attribute in Dataverse / Dynamics 365

string ConnectionString = "AuthType = OAuth; " +
                  "AppId=51f81489-12ee-4a9e-aaae-a2591f45987d; " +
                  "Username=user@domain.onmicrosoft.com; " +
                  "Password=pwd; " +
                  "RedirectUri=app://58145B91-0C36-4500-8554-080854F2AC97;" +
                  "Url = https://orgname.crm4.dynamics.com/;";


 CrmServiceClient svc = new CrmServiceClient(ConnectionString);

            if (svc.IsReady)
            {
                // Create PolymorphicLookupAttribute 
                // with mycustomtable custom entity / table
                // referencing case, contact and account entity
                var varOrgRequest = new OrganizationRequest();

                // specify the request name
                varOrgRequest.RequestName = "CreatePolymorphicLookupAttribute";

                // specify lookup attribute details
                varOrgRequest.Parameters["Lookup"] = new LookupAttributeMetadata()
                {
                    SchemaName = "crf82_mypolymorphiclookup",
                    DisplayName = new Label("My Polymorphic Lookup", 1033)
                };

                // referencing entity is our custom entity named my custom table
                // referenced entity is incident
                var oneToManyRelation1 = new OneToManyRelationshipMetadata();
                oneToManyRelation1.ReferencingEntity = "crf82_mycustomtable";
                oneToManyRelation1.ReferencedEntity = "incident";
                oneToManyRelation1.SchemaName = "crf82_mycustomtable_crf82_incident";

                // referencing entity is our custom entity named my custom table
                // referenced entity is contact
                var oneToManyRelation2 = new OneToManyRelationshipMetadata();
                oneToManyRelation2.ReferencingEntity = "crf82_mycustomtable";
                oneToManyRelation2.ReferencedEntity = "contact";
                oneToManyRelation2.SchemaName = "crf82_mycustomtable_crf82_contact";


                // referencing entity is our custom entity named my custom table
                // referenced entity is account
                var oneToManyRelation3 = new OneToManyRelationshipMetadata();
                oneToManyRelation3.ReferencingEntity = "crf82_mycustomtable";
                oneToManyRelation3.ReferencedEntity = "account";
                oneToManyRelation3.SchemaName = "crf82_mycustomtable_crf82_account";

                // populate OneToManyRelationships parameter of CreatePolymorphicLookupAttribute request
                varOrgRequest.Parameters["OneToManyRelationships"] = new OneToManyRelationshipMetadata[]
                {
                    oneToManyRelation1, oneToManyRelation2, oneToManyRelation3
                };

                // specify the existing solution name 
                varOrgRequest.Parameters["SolutionUniqueName"] = "MySolution";

                var response = svc.Execute(varOrgRequest);
            }

                var createOneToManyRelationshipRequest = new CreateOneToManyRequest();

                // referencing entity is our custom entity named mycustomtable
                // referenced entity is contact - add the entity to be added
                var oneToManyRelationAdd = new OneToManyRelationshipMetadata();
                oneToManyRelationAdd.ReferencingEntity = "crf82_mycustomtable";
                oneToManyRelationAdd.ReferencedEntity = "contact";
                oneToManyRelationAdd.SchemaName = "crf82_mycustomtable_crf82_contact";

                createOneToManyRelationshipRequest.OneToManyRelationship = oneToManyRelationAdd;


                // specify lookup attribute details to which new relationship is to be added
                createOneToManyRelationshipRequest.Parameters["Lookup"] = new LookupAttributeMetadata()
                {
                    SchemaName = "crf82_mypolymorphiclookup",
                    DisplayName = new Label("My Polymorphic Lookup", 1033)
                };


                var createOneToManyRelationshipResponse = svc.Execute(createOneToManyRelationshipRequest);

 var deleteRelationShip = new DeleteRelationshipRequest();
                // specify schema name of the relationship 
                deleteRelationShip.Name = "crf82_mycustomtable_crf82_contact1";
                svc.Execute(deleteRelationShip);

  // User delete attribute request 
                DeleteAttributeRequest varDelRequest = new DeleteAttributeRequest();

                // specify the entity name
                varDelRequest.EntityLogicalName = "crf82_mycustomtable";

                // specify the schema name of the entity
                varDelRequest.LogicalName = "crf82_mymultitablelookup";
                svc.Execute(varDelRequest);