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);
}
}