I have this extension method in my .NET code check if a string is something:

public static bool IsSomething(this string text)
{
   var isNothing = string.IsNullOrEmpty(text) || string.IsNullOrWhiteSpace(text);
   return !isNothing;
}

However, I can't use it in my EF Core quereis:

dbset.Where(i => i.Title.IsSomething()); // throws non-translatable error

I know that I can rewrite my query as:

dbset.Where(i => i.Title != null && i.Title.Trim() != ""); // this works, but it's too verbose

But I really don't want to write that long non-descriptive code.

How can I have IsSomething to be translatable for SQL Server?

CodePudding user response：

Just use IsNullOrWhiteSpace; it does what IsNullOrEmpty does:

Return true if the value parameter is null or Empty, or if value consists exclusively of white-space characters. -- documentation for IsNullOrWhiteSpace

And it is mapped by EF Core to an SQL of

@value IS NULL OR LTRIM(RTRIM(@value)) = N''

This means your IsSonething method is effectively !IsNullOrWhiteSpace, which EF will translate if you use

CodePudding user response：

You cannot translate this method to SQL Server. However, you can use a method that returns Expression. For example:

public static Expression<Func<Student, bool>> IsSomething()
{
    return (s) => string.IsNullOrEmpty(s.FirstName) || string.IsNullOrWhiteSpace(s.FirstName);
}

Usually, you should call AsEnumerable before using methods:

dbset.AsEnumerable().Where(i => i.Title.IsSomething());

But it will load all entities from data base.