如何将SqlType本地转换为基础SQL类型声明？

Question

Is there a way in .NET SqlClient to translate SqlType to actual SQL type declaration, like

SqlInt32  -> "int"
SqlGuid   -> "uniqueidentifier"
SqlXml    -> "xml"
SqlString -> "nvarchar(??)"

without doing it manually?

CLARIFICATION: I am trying to automatically refactor a number of SQL select statements, and I need to know what types do they return. I'm planning to do it by running following code:

using (var connection = new SqlConnection(SqlConnectionString))
{
    connection.Open();
    var command = connection.CreateCommand();
    command.CommandText = sql;
    var reader = command.ExecuteReader(CommandBehavior.SchemaOnly);
    for (int i = 0; i < reader.FieldCount; ++i)
    {
         var type = reader.GetProviderSpecificFieldType(i);
         ... generate some sql code ...
    }
}

So, once I got the type, I'm trying to generate some SQL code and use SqlTye returned in GetProviderSpecificFieldType, and I wanted to see if there's already a function I can use that will take SqlType and give me back the SQL declaration

Answer 1

Not that I know of. Since there is no 1:1 correspondence (for example, an SqlString can correspond to the SQL Server types char , nchar , text , ntext , nvarchar and varchar ), such a function would have to guess what the original type was, since this information is no longer available once you got the SqlString .

If you know that an SqlString always corresponds to an nvarchar(255) in your database, you can write such a function yourself, using this list as a starting point.

What are you trying to achieve? Maybe there is better solution to your problem...

Answer 2

这可以帮到你

Answer 3

I found a solution. I used GetSchemaTable in order to get the details of SQL type:

    private string __type(SqlDataReader reader, int i)
    {
        var schema = reader.GetSchemaTable();
        var row = (from DataRow r in schema.Rows 
                   where (int)r["ColumnOrdinal"] == i 
                   select r).First();

        var type = (string) row["DataTypeName"];
        if (type == "nvarchar" || type == "varchar" || 
            type == "nchar" || type == "char")
        {
            int maxLength = (int) row["ColumnSize"];
            if (maxLength == 2147483647) maxLength = -1;
            type += string.Format("({0})", (maxLength > 0) ? 
                        (object) maxLength : (object) "max");
        }
        return type;
    }

Answer 4

Not quite a total duplicate but there is the opposite direction .

The problem of it being a Many <-> Many mapping is exactly the same though.

Any fully automatic translation would be, at best overzealous (for example mapping any string to a TEXT column), and at worst wrong in some subtle way.

At the very least it would need to be Version dependent, for example should it use DateTime or DateTime2?