Anyway, one of the tricks I couldnt post was how to retrieve a Lookup which is little tricky. Lets check it using with examples.
Here I am trying to retrieve Full Name and Email Address as below.
https://xxxx.crm6.dynamics.com/api/data/v9.1/contacts(73bc115c-4317-ea11-a811-000d3a6aa9c8)?$select=fullname,emailaddress1
It works fine. Check my result.
{"@odata.context":"https://xxxx.crm6.dynamics.com/api/data/v9.1/$metadata#contacts(fullname,emailaddress1)/$entity","@odata.etag":"W/\"77570311\"","fullname":"Aaron Smith","emailaddress1":null,"contactid":"73bc115c-4317-ea11-a811-000d3a6aa9c8"}
Suppose, I need to retrieve a lookup field value. For example, Created By name. What I feel is just adding it as another field. So I am adding to the end of he field list.
https://xxxx.crm6.dynamics.com/api/data/v9.1/contacts(73bc115c-4317-ea11-a811-000d3a6aa9c8)?$select=fullname,emailaddress1,createdby
Hmm.. here comes the confusion. I don't get any values for Created By lookup field. I am sure I spelled correctly, otherwise I would get a error message about unknown field.
{"@odata.context":"https://xxxx.crm6.dynamics.com/api/data/v9.1/$metadata#contacts(fullname,emailaddress1,createdby)/$entity","@odata.etag":"W/\"77570311\"","fullname":"Aaron Smith","emailaddress1":null,"contactid":"73bc115c-4317-ea11-a811-000d3a6aa9c8"}
Well, this is the trick WebApi just doesn't return values from other entities. Lookup value is physically in related entity. So you have to extend the query with Expand keyword.
https://xxxx.crm6.dynamics.com/api/data/v9.1/contacts(73bc115c-4317-ea11-a811-000d3a6aa9c8)?$select=fullname,emailaddress1&$expand=createdby($select=fullname,systemuserid)
Here we get the result like a charm.
{"@odata.context":"https://xxxx.crm6.dynamics.com/api/data/v9.1/$metadata#contacts(fullname,emailaddress1,createdby(fullname,systemuserid))/$entity","@odata.etag":"W/\"77570311\"","fullname":"Aaron Bailey","emailaddress1":null,"contactid":"73bc115c-4317-ea11-a811-000d3a6aa9c8","createdby":{"@odata.etag":"W/\"29915606\"","fullname":"Paul Wicks","systemuserid":"267874e4-645c-e911-a870-000d3a6a065c","ownerid":"267874e4-645c-e911-a870-000d3a6a065c"}}
In summery, make sure you link entity with Expand command to retrieve lookup values.
Simple!
