Gabriel Bogéa Perez

I have a group of classes that I build to get metadata from the database to use with my code generators. The class has the following structure:

public class ConstraintMetadata
{
    public string ConstraintName { get; set; }

    public string ColumnName { get; set; }

    public string ConstraintType { get; set; }

    public string TableName { get; set; }
}

I wanted to write a group by clause using Linq to group the objects I retrieved from the db by TableName, ConstraintName and ConstraintType. This would allow me to have one object for each constraint with a list of all the columns. Since Linq only allows one object in the group by clause the way out is to create an anonymous object with all the properties I want.

var constraints = from c in constraintsMetadata
                  group c by new
                             {
                                 c.TableName, 
                                 c.ConstraintType, 
                                 c.ConstraintName
                             } into g
                      select new
                      {
                          g.Key.ConstraintName,
                          g.Key.ConstraintType,
                          g.Key.TableName,
                          Columns = g.Select(x=>x.ColumnName).ToList()
                      };

Now, if I want to get all the constraints for a table and print it to the console window I can do this:

var tableConstraints = constraints.Where(x => x.TableName == table.Name);

foreach (var tableConstraint in tableConstraints)
{
    Console.Out.WriteLine("Constraint Name:{0}, Table:{1}, Type:{2} Columns:", 
        tableConstraint.ConstraintName , 
        tableConstraint.TableName, 
        tableConstraint.ConstraintType);
    foreach (var column in tableConstraint.Columns)
    {
        Console.Out.WriteLine(column);
    }
}