Is there a built-in class in the .Net framework that can be used to denote an AnsiString?

Question

For dapper I need to build support for passing in AnsiString params.

Databases have both unicode and non-unicode strings, picking the right parameter type is sometimes crucial.

DbType.String vs DbType.AnsiString for a particular param can heavily effect perf.

In dapper we pass in parameters dynamically, Eg:

Query<User>("select * from Users where Name=@Name", new {Name = "name"});

I have an internal map that says that if I see typeof(String) I know to pass in the param as a DbType.String

However, I would like my users to be able to denote that the string should be an AnsiString. Attributes are not supported for anonymous classes, so I need a distinct type for this.

Clearly I can invent one:

public class AnsiString 
{
    private readonly string str;
    public AnsiString(string str)
    {
        this.str = str;
    }

    public String Value { get { return str; } }
}

Which would give me the clean API:

Query<User>("select * from Users where Name=@Name", 
   new {Name = new AnsiString("name")});

However, why invent one if such a class exists in System.Data or the BCL.

Is there a type somewhere in the BCL or System.Data I could use as a container for AnsiString, with similar semantics to the sample above?

Answer 1

There is not such class in the BCL or System.Data, you will have to roll your own.

We went with a custom type to provide more fine-grained customn in the end; this test shows typical usage:

public void TestDbString()
{
    var obj = connection.Query("select datalength(@a) as a, datalength(@b) as b, datalength(@c) as c, datalength(@d) as d, datalength(@e) as e, datalength(@f) as f",
        new
        {
            a = new DbString { Value = "abcde", IsFixedLength = true, Length = 10, IsAnsi = true },
            b = new DbString { Value = "abcde", IsFixedLength = true, Length = 10, IsAnsi = false },
            c = new DbString { Value = "abcde", IsFixedLength = false, Length = 10, IsAnsi = true },
            d = new DbString { Value = "abcde", IsFixedLength = false, Length = 10, IsAnsi = false },
            e = new DbString { Value = "abcde", IsAnsi = true },
            f = new DbString { Value = "abcde", IsAnsi = false },
        }).First();
    ((int)obj.a).IsEqualTo(10);
    ((int)obj.b).IsEqualTo(20);
    ((int)obj.c).IsEqualTo(5);
    ((int)obj.d).IsEqualTo(10);
    ((int)obj.e).IsEqualTo(5);
    ((int)obj.f).IsEqualTo(10);
}

So; it supports:

• ansi vs unicode
• fixed vs dynamic length
• in the case of dynamic length, explict vs implicit (4000 if the length is <= 4000; "max" otherwise - this keeps the number of query-plans sane)

The type is available inside dapper.

Answer 2

I guess you can use string for DbType.String and char[] for DbType.AnsiString.

It will look very similar to your current code:

Query<User>("select * from Users where Name=@Name", new {Name = "name".ToCharArray()});

Or if you wan use your AnsiString, you can create extension method .ToAnsiString():

public static AnsiString( this string s ) { return new AnsiString(s); }
Query<User>("select * from Users where Name=@Name", new {Name = "name".ToAnsiString()});