ServiceStack ORMLite - Select columns

Question

I recently started working with ServiceStack and its ORMLite framework. I have searched on Google and browsed the source code but couldn't find anything relevent.

Is there any way to select specific columns when executing a query with ORMLite ? Something like that : Db.First<Model>(q => q.Id == someId, "Column1, Column2")

Unless I missed this feature, I am surprised nobody asked about this before, since this is one the rule of thumbs to optimize your DB transactions.

Answer 1

If you want to specify columns other that the table you need to use SQL as seen in this earlier example

So in your case you could do something like:

Db.First<Model>("SELECT Column1, Column2 FROM AnyTableOrView");

You can also create a partial model that looks at your table by decorating it with the [Alias] attribute, like:

[Alias("AnyTableOrView")]
public class Model {
    public int Id { get; set; }
    public string Column1 { get; set; }
    public string Column2 { get; set; }
}

Then you can do something like:

Db.First<Model>(q => q.Id == someId);

And it will only SELECT + populate fields from the partial model.

Answer 2

I did try this :

1. Created a Database VIEW (table name and columns are already set)
2. Created a class named "Event" and matching each fields for that table with a property (i used [Alias] for table name and for all columns to have nice names)

3. Wrote access to DB to select 1 record based on it's ID

       var dbFactory = new OrmLiteConnectionFactory(
           "Data Source=MyDB;User Id=user;Password=pwd",  // Connection String
           OracleDialect.Provider);
   
       using (var db = dbFactory.OpenDbConnection())
       {
               var event = db.GetByIdOrDefault<Event>( request.Id );
       }
   

At that point the var 'event' is populated but only the Id field is filled ! all the others fields of the class are not filled (while there are really data in database).

It's the simplest i can do and it does not work. Any ideas ? (PS : i am using OrmLite for Oracle)

Thanks

Answer 3

I have found the problem. It was due to an incorrect type matching between field in my class (defined as a string) and the corresponding Oracle Field (that is a DATE).

I replaced the string with datetime and worked like a charm.

So it's working perfectly with a VIEW and that's GREATLY simplify the code.

Answer 4

I had a similar problem, however my solution was different.

I had a int property in my POCO. My query (from Oracle) was returning a null for this property. It caused a exception to be raised and prevented further processing of that row. The result was a partial populated POCO.

The solution was to change to type to be nullable.

public int? mypropperty