.net – LINQ to Entities does not recognize the method System.String

c#-4.0linqlinq-to-entitiesnet

I keep getting this error message from the code below. What am I doing wrong?

LINQ to Entities does not recognize the method 'System.String ToString(System.Object)' method, and this method cannot be translated into a store expression.

var pros = from programs in db.Programs
           select new {
               programs.ProgramID,
              val = (programs.ProgramShortName + " On: " +  (Convert.ToString(programs.ProgramStartDate) ?? ""))
                           };

lbPrograms.DataTextField = "val";
lbPrograms.DataValueField = "ProgramID";
lbPrograms.DataSource = pros;
lbPrograms.DataBind();

Best Answer

It doesn't recognise string Convert.ToString(object)... so... don't use that. You could try .ToString() directly, but frankly I would just select:

...
select new {
          programs.ProgramID,
          programs.ProgramShortName,
          programs.ProgramStartDate }

and worry about any stringification locally. Or at least a separate projection (noting that AsEnumerable() changes this from composition to deferred iteration):

var formatted = from programs in pros.AsEnumberable()
                select new {
                 programs.ProgramID,
                 val = (programs.ProgramShortName
        + " On: " +  (Convert.ToString(programs.ProgramStartDate) ?? "")) };

and then bind to formatted. This will do a query on the 3 columns, but format locally.

Note:

Make sure you also check out Alex's answer regarding the SqlFunctions helper class that was added later. In many cases it can eliminate the need for the temporary variable.

.net – LINQ to Entities does not recognize the method

As you've figured out, Entity Framework can't actually run your C# code as part of its query. It has to be able to convert the query to an actual SQL statement. In order for that to work, you will have to restructure your query expression into an expression that Entity Framework can handle.

public System.Linq.Expressions.Expression<Func<Charity, bool>> IsSatisfied()
{
    string name = this.charityName;
    string referenceNumber = this.referenceNumber;
    return p => 
        (string.IsNullOrEmpty(name) || 
            p.registeredName.ToLower().Contains(name.ToLower()) ||
            p.alias.ToLower().Contains(name.ToLower()) ||
            p.charityId.ToLower().Contains(name.ToLower())) &&
        (string.IsNullOrEmpty(referenceNumber) ||
            p.charityReference.ToLower().Contains(referenceNumber.ToLower()));
}

Best Answer

Related Solutions

C# – LINQ to Entities does not recognize the method ‘System.String ToString()’ method, and this method cannot be translated into a store expression

Note:

.net – LINQ to Entities does not recognize the method

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