Retrieve Account Number using account GUID in Dynamics CRM

Question

I'm new to LINQ so please apology if I ask wrong question. I want to retrieve account number in Dynamics CRM using account GUID and LINQ. But unable to find. I've following snippet but gives me exception that specified cast is not valid

 accountID = (Guid)contact["parentcustomerid"];
 var account = from a in context.CreateQuery("account")
 where a.GetAttributeValue<Guid?>("accountid") == accountID
 select new {accountNumber = a["accountnumber"] };

Answer 1

What is accountID ? Guid or Nullable<Guid>

try below snippet:

accountID = (Guid)contact["parentcustomerid"];
var account = from a in context.CreateQuery("account")
where a.GetAttributeValue<Guid>("accountid") == accountID
select new {accountNumber = a.GetAttributeValue<int>("accountnumber") };

you can use Query Expression . It is very easy to use:

QueryExpression queryExpression = new QueryExpression("account");
queryExpression.ColumnSet = new ColumnSet("accountnumber");
queryExpression.Criteria.AddCondition("accountid", ConditionOperator.Equal, accountID);

Or

_service.Retrieve("account", accountID, new ColumnSet("accountnumber"));

Answer 2

Try something like following:

var accountID = contact.GetAttributeValue<EntityReference>("parentcustomerid").Id;

var accountnumber = (from a in context.CreateQuery("account")
 where a.GetAttributeValue<Guid>("accountid") == accountID
 select a.GetAttributeValue<string>("accountnumber")).FirstOrDefault();