Using reflection to address a Linqed property

Question

I\'m trying to writing a generic method that will load a record of a specific type, with a specific ID. Here\'s one way that works:

    public abstract clas         


        

Answer 1

Having read these posts: Generic Data Access using LINQ to SQL and C#, LINQ-to-SQL: Generic Primary Key function and Calling a generic method with Type

My colleague and I came up with the following digest:

We added the following method to our datacontext (in a partial class).

public T GetInstanceByPrimaryKey(object primaryKeyValue) where T : class
{
    var table = this.GetTable();
    var mapping = this.Mapping.GetTable(typeof(T));
    var pkfield = mapping.RowType.DataMembers.SingleOrDefault(d => d.IsPrimaryKey);

    if (pkfield == null)
        throw new Exception(String.Format("Table {0} does not contain a Primary Key field", mapping.TableName));

    var param = Expression.Parameter(typeof(T), "e");

    var predicate =
        Expression.Lambda>(Expression.Equal(Expression.Property(param, pkfield.Name), Expression.Constant(primaryKeyValue)), param);

    return table.SingleOrDefault(predicate);
}

Then, where we need to instanciate from the type name and primary key value:

string name = "LinqObjectName";
int primaryKey = 123;

var dc = new YourDataContext();

Type dcType = dc.GetType();
Type type = dcType.Assembly.GetType(String.Format("{0}.{1}", dcType.Namespace, name));

MethodInfo methodInfoOfMethodToExcute = dc.GetType().GetMethod("GetInstanceByPrimaryKey");
MethodInfo methodInfoOfTypeToGet = methodInfoOfMethodToExcute.MakeGenericMethod(name);
var instance = methodInfoOfTypeToGet.Invoke(dc, new object[] { primaryKey });

return instance;

Hope this helps!