Posts tagged with linq - page 5

LINQ to SQL log to debug window, file, memory or multiple writers

The Log property on a LINQ to SQL data context takes a TextWriter and streams out details of the SQL statements and parameters that are being generated and sent to the server.

Normally in examples you will see Console.Out being assigned to it which is fine for small demos and sandboxes but sooner or later you’ll want access to it in Windows or web applications. Here are some examples of how to redirect TextWriter output such as the DataContext log to other destinations.

Github has the latest version of ActionTextWriter etc.

To the output/debug window

The output/debug window mechanism actually uses a listener mechanism and so doesn’t actually directly expose a TextWriter interface however we can simply wrap up Debug.Write in something that does and use that instead:

class DebugTextWriter : System.IO.TextWriter {
   public override void Write(char[] buffer, int index, int count) {
       System.Diagnostics.Debug.Write(new String(buffer, index, count));

   public override void Write(string value) {

   public override Encoding Encoding {
       get { return System.Text.Encoding.Default; }

To use it then simply:

myDataContext.Log = new DebugTextWriter();

To a file

 db.Log = new System.IO.StreamWriter("linq-to-sql.log") { AutoFlush = true };

If you wish to not overwrite the existing log file then change the constructor to include the parameter true after the filename. Bear in mind this log file can get very large and slow down your application with all that extra writing to disk and could well reveal information you’d rather wasn’t persisted there so the DEBUG conditional is recommended.

To memory

 var sw = new System.IO.StringWriter();
 db.Log = sw;

You will be able to examine sw or call ToString() on it to see the contents. Again this is not recommended for production as it will cause a lot of memory consumption as the StringWriter gets larger and larger.

To multiple writers

Here is a small useful class that lets you send the results intended for a TextWriter off into multiple writers.

class MulticastTextWriter : TextWriter {
  private readonly IList<TextWriter> textWriters;

  public MulticastTextWriter() : this(new List<TextWriter>()) {

  public MulticastTextWriter(IList<TextWriter> textWriters) {
    this.textWriters = textWriters;

  public void Add(TextWriter textWriter) {
    lock (textWriters)

  public bool Remove(TextWriter textWriter) {
    lock (textWriters)
      return textWriters.Remove(textWriter);

  public override void Write(char[] buffer, int index, int count) {
    lock (textWriters)
      foreach (TextWriter textWriter in textWriters)
        textWriter.Write(buffer, index, count);

  public override Encoding Encoding {
    get { return System.Text.Encoding.Default; }

So if you wanted to output to a log and also to the debug window, you would use it like this (again recommended only for debugging):

var mw = new MulticastTextWriter();
mw.Add(new DebugTextWriter());
mw.Add(new System.IO.StreamWriter("linq-to-sql.log") { AutoFlush = true });
db.Log = mw;

Anything you want

To wrap things up here is a small TextWriter that lets you go off and do whatever you like with the string via the Action delegate.

class ActionTextWriter : TextWriter {
  private readonly Action<string> action;

  public ActionTextWriter(Action<string> action) {
    this.action = action;

  public override void Write(char[] buffer, int index, int count) {
    Write(new string(buffer, index, count));

  public override void Write(string value) {

  public override Encoding Encoding {
    get { return System.Text.Encoding.Default; }

So if you wanted to output all log information to say a WinForms message box a tiny lambda expression gets you there:

db.Log = new ActionTextWriter(s => MessageBox.Show(s));

Have fun!


LINQ to SQL T4 template reloaded

A newer version of this LINQ to SQL template is available.

The topic of modifying the code generation phase of LINQ to SQL comes up quite often and the limited T4 template I published here last month was good at showing the potential but wasn’t a practical replacement for the code generation phase.

I am please to make available the next version, which now…

  • Runs from the DBML therefore keeping the designer in the loop
  • Generate all the attributes for columns and tables including UpdateCheck, IsDbGenerated etc.
  • Supports associations including those with a foreign key
  • Generates appropriate attributes and code for both serialization modes

In short it generates code that is now functionally equivalent to SQL Metal with the following caveats:

  • C# only – VB.NET can be added if there is some interest
  • Stored procedures – not yet supported
  • Table inheritance – incomplete
  • DBML changes require you open and re-save the T4 template so it regenerates the code
  • Unidirectional serialization requires you add System.Runtime.Serialization to your project references (thanks Roger!)

To use the template:

  • Extract the archive and add the two files to your project
  • Right-click on the file, choose Properties and set the Custom Tool to blank
  • Rename to the same name as your DBML file (but keeping the .tt extension) and open it
  • Click save and watch a freshly generate C# DataContext pop out
  • Switch off the LINQ to SQL designer generated C# by either setting the Custom Tool on the DBML to blank or setting the Build Action on the generated C# to None. contains a lightweight wrapper around the DBML which is processed using LINQ to XML making the template easier to work with and providing a central for naming rules etc.

This code should be treated as a sample and hasn’t received much testing yet so feel free to leave comments or feedback here.

Some places you could take this template:

  • Generate an interface for your data context to improve mocking
  • Alternative naming and defaults
  • Splitting output into multiple files
  • New languages


Experimental LINQ to SQL template

A newer version of this LINQ to SQL template is available.

While SQLMetal does a good job of turning your SQL schema into a set of classes for you it doesn’t let you customize the code generation process.

Usefully there is now a templating system built into Visual Studio 2008 called Text Templates (T4 for short).

Here is a short (369 line) experimental proof-of-concept T4 template I wrote last night that will generate a data context and associated entity classes as a starting point similar to that produced by SQLMetal.

Download of this old version no longer available, see the newer article!

Once downloaded unzip and drop the into your project and edit line 17 to set the connection string. You can also edit lines 18 and 19 to set the namespace and class name. The lightweight wrappers around database, table and column can be found at the end of the file – they simply wrap the SQL Server Information_Schema views as briefly as possible.

Within seconds Visual Studio should have created a code-behind file for the DataContext named DataContext.cs.cs with your generated code ready to use :) If you don’t like the way the template generates your context you can change it :)

There are limitations with this experimental proof-of-concept including: </p>
  • Processes all and only tables in the database (no views or SP’s)
  • Foreign-key relationships are not implemented
  • Column attributes for IsDbGenerated, UpdateCheck and AutoSync not implemented
  • C# only (sorry Julie)
  • Plural and singular naming rules are incomplete
  • Can’t modify schema as you could with a designer stage
To learn more about T4: </p>


Using LINQ to foreach over an enum in C#

I can’t be the only person in the world who wants to foreach over the values of an enum otherwise Enum.GetValues(Type enumType) wouldn’t exist in the framework. Alas it didn’t get any generics love in .NET 2.0 and unhelpfully returns an array.

Thanks to the power of LINQ you can do this:

foreach(var customerType in Enum.GetValues(typeof(CustomerTypes)).Cast<CustomerTypes>()))

That is okay, but this is more concise:

foreach(CustomerTypes customerType in Enums.Get<CustomerTypes>())

The tiny class to achieve that is, of course:

using System.Collections.Generic;
using System.Linq;

public static class Enums {
  public static IEnumerable<T> Get<T>() {
    return System.Enum.GetValues(typeof(T)).Cast<T>();