Linq to SQL Join and Contains Operators
in the following query
var restrictions = from p in dcTrad.quop_restricted_items
where p.entry_status == 'P' && p.batch == "PRODUCTION" && p.problem != null
from q in dcTrad.model_companies
where q.co_name != null && p.brimsec == q.primary_bsec
select new { Company = q.co_name, Restriction = p.comment ?? "Restricted without comments", Portfolio = p.problem };
I need to replace
p.brimsec == q.primary_bsec
with
p.开发者_如何学编程brimsec.StartsWith ( q.primary_bsec )
but I get the following error:
Only arguments that can be evaluated on the client are supported for the String.StartsWith method
How can I make this work?
Unfortunately the LINQ to SQL translator is not smart enough to translate this code, but there's a trick that achieves the same:
p.brimsec.StartsWith ( q.primary_bsec )
Translates to:
p.brimsec.SubString(0, q.primary_bsec.Length) == q.primary_bsec
The LINQ to SQL translator handles this just fine, and the semantics are equivalent to StartsWith.
Frankly, I don't see why translating StartsWith properly for server-side arguments was so hard that the LINQ developers just decided to throw an error instead.
Basically the linq to sql does not know how to convert startswith to Sql. This is because internally at run time your linq is code generated to sql.
You may go about achieving this by creating a UDF (user defined function in sql) and using it from your linq statement.
The article is as below: http://msdn.microsoft.com/en-us/library/bb399416.aspx
Andrew
I think the problem you're running into is that linq-to-sql has no translation of String.StartsWith into SQL. String.Contains does work, though - you'd need to go through your resultant collection and filter out the items that don't start with q.primary_bsec.
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