C# – LINQ to Entities does not recognize the method ‘System.String Format

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How can i refactor this LINQ to make this work?

var a =  (from app in mamDB.Apps where app.IsDeleted == false 
                select string.Format("{0}{1}",app.AppName, 
                app.AppsData.IsExperimental? " (exp)": string.Empty))
               .ToArray();}

I now get error:

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

I have uselessly tried:

return (from app in mamDB.Apps where app.IsDeleted == false 
        select new string(app.AppName + (app.AppsData != null && 
        app.AppsData.IsExperimental)? " (exp)": string.Empty)).ToArray();

Best Answer

You can do the string.Format back in LINQ-to-Objects:

var a =  (from app in mamDB.Apps where app.IsDeleted == false 
         select new {app.AppName, app.AppsData.IsExperimental})
         .AsEnumerable()
         .Select(row => string.Format("{0}{1}",
            row.AppName, row.IsExperimental ? " (exp)" : "")).ToArray();

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

Just save the string to a temp variable and then use that in your expression:

var strItem = item.Key.ToString();

IQueryable<entity> pages = from p in context.pages
                           where  p.Serial == strItem
                           select p;

The problem arises because ToString() isn't really executed, it is turned into a MethodGroup and then parsed and translated to SQL. Since there is no ToString() equivalent, the expression fails.

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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