Posts tagged with linq - page 2

Multiple outputs from T4 made easy – revisited

My multiple outputs from t4 made easy post contained a class making it easy to produce multiple files from Visual Studio’s text templating engine (T4).

While useful it had a few issues:

  • Getting start/end blocks mixed up resulted in unpredictable behavior
  • Files were rewritten even when content did not change
  • Did not play well with source control
  • Files not always deleted in VS
  • Failed in Visual Studio’s project-less Web Sites

This helper class forms the basis of multiple file output for Entity Framework templates in .NET 4.0 and the LINQ to SQL templates on CodePlex so we (Jeff Reed, Andrew Peters and myself) made the following changes.


Simpler block handling

The header, footer and file blocks can now be completed with EndBlock (EndHeader and EndFooter are gone), although it will automatically end the previous block when it hits a new one or the final Process method.

Skip unchanged files

Files are now only written to disk if the contents are different with the exception of the original T4 output file (we can’t stop that, sorry).

There is additional overhead reading and comparing files we believe unmodified files keeping their dates and source control status are worth it.

Automatic checkout

When the template detects it is running in Visual Studio and that the file it needs to write to is currently in source control but not checked out it will check the file out for you.

Predictable clean-up

All files that were not part of the generation process but are nested under the project item will now be deleted when running inside Visual Studio.

Outside of Visual Studio files are no longer deleted – this was destructive and it couldn’t know which files it generated on a previous run to clean-up correctly anyway.

Website projects fall back to single file generation

Visual Studio has both web sites and web applications with the former being project-less leading to very messy multi-file generation so it forces single file generation.

Internal improvements

Source is now simpler to read and understand with less public visibility and faster and more robust VS interop by batching the files & deletes to a single invoke at the end to avoid conflicts with other add-ins that might be triggered by the changes.



You’ll need to get the code into your template – either copy the code in or reference it with an include directive. Then declare an instance of the Manager class passing in some environmental options such as the desired default output path. (For Visual Studio 2010 remove the #v3.5 portion from the language attribute)

<#@ template language="C#v3.5" hostspecific="True"
#><#@include file="Manager.ttinclude"
#><# var manager = Manager.Create(Host, GenerationEnvironment); #>

File blocks

Then add one line before and one line after each block which could be split out into it’s own file passing in what the filename would be if split. The EndBlock is optional if you want it to carry through to the next one :)

<# manager.StartNewFile("Employee.generated.cs"); #>
public class Employee {  }
<# manager.EndBlock(); #>

Headers & footers

Many templates need to share a common header/footer for such things as comments or using/import statements or turning on/off warnings. Simply use StartHeader and StartFooter and the blocks will be emitted to the start and end of all split files as well as being left in the original output file.

<# manager.StartHeader(); #>
// Code generated by a template
using System;

<# manager.EndBlock(); #>


At the end of the template call Process to handle splitting the files (true) or not (false). Anything not included in a specific StartNewFile block will remain in the original output file.

<# manager.Process(true); #>

Revised Manager class

Latest source available at GitHub
<#@ assembly name="System.Core"
#><#@ assembly name="System.Data.Linq"
#><#@ assembly name="EnvDTE"
#><#@ assembly name="System.Xml"
#><#@ assembly name="System.Xml.Linq"
#><#@ import namespace="System"
#><#@ import namespace="System.CodeDom"
#><#@ import namespace="System.CodeDom.Compiler"
#><#@ import namespace="System.Collections.Generic"
#><#@ import namespace="System.Data.Linq"
#><#@ import namespace="System.Data.Linq.Mapping"
#><#@ import namespace="System.IO"
#><#@ import namespace="System.Linq"
#><#@ import namespace="System.Reflection"
#><#@ import namespace="System.Text"
#><#@ import namespace="System.Xml.Linq"
#><#@ import namespace="Microsoft.VisualStudio.TextTemplating"

// Manager class records the various blocks so it can split them up
class Manager {
    private class Block {
        public String Name;
        public int Start, Length;

    private Block currentBlock;
    private List<Block> files = new List<Block>();
    private Block footer = new Block();
    private Block header = new Block();
    private ITextTemplatingEngineHost host;
    private StringBuilder template;
    protected List<String> generatedFileNames = new List<String>();

    public static Manager Create(ITextTemplatingEngineHost host, StringBuilder template) {
        return (host is IServiceProvider) ? new VSManager(host, template) : new Manager(host, template);

    public void StartNewFile(String name) {
        if (name == null)
            throw new ArgumentNullException("name");
        CurrentBlock = new Block { Name = name };

    public void StartFooter() {
        CurrentBlock = footer;

    public void StartHeader() {
        CurrentBlock = header;

    public void EndBlock() {
        if (CurrentBlock == null)
        CurrentBlock.Length = template.Length - CurrentBlock.Start;
        if (CurrentBlock != header && CurrentBlock != footer)
        currentBlock = null;

    public virtual void Process(bool split) {
        if (split) {
            String headerText = template.ToString(header.Start, header.Length);
            String footerText = template.ToString(footer.Start, footer.Length);
            String outputPath = Path.GetDirectoryName(host.TemplateFile);
            foreach(Block block in files) {
                String fileName = Path.Combine(outputPath, block.Name);
                String content = headerText + template.ToString(block.Start, block.Length) + footerText;
                CreateFile(fileName, content);
                template.Remove(block.Start, block.Length);

    protected virtual void CreateFile(String fileName, String content) {
        if (IsFileContentDifferent(fileName, content))
            File.WriteAllText(fileName, content);

    public virtual String GetCustomToolNamespace(String fileName) {
        return null;

    public virtual String DefaultProjectNamespace {
        get { return null; }

    protected bool IsFileContentDifferent(String fileName, String newContent) {
        return !(File.Exists(fileName) && File.ReadAllText(fileName) == newContent);

    private Manager(ITextTemplatingEngineHost host, StringBuilder template) { = host;
        this.template = template;

    private Block CurrentBlock {
        get { return currentBlock; }
        set {
            if (CurrentBlock != null)
            if (value != null)
                value.Start = template.Length;
            currentBlock = value;

    private class VSManager: Manager {
        private EnvDTE.ProjectItem templateProjectItem;
        private EnvDTE.DTE dte;
        private Action<String> checkOutAction;
        private Action<IEnumerable<String>> projectSyncAction;

        public override String DefaultProjectNamespace {
            get {
                return templateProjectItem.ContainingProject.Properties.Item("DefaultNamespace").Value.ToString();

        public override String GetCustomToolNamespace(string fileName) {
            return dte.Solution.FindProjectItem(fileName).Properties.Item("CustomToolNamespace").Value.ToString();

        public override void Process(bool split) {
            if (templateProjectItem.ProjectItems == null)
            projectSyncAction.EndInvoke(projectSyncAction.BeginInvoke(generatedFileNames, null, null));

        protected override void CreateFile(String fileName, String content) {
            if (IsFileContentDifferent(fileName, content)) {
                File.WriteAllText(fileName, content);

        internal VSManager(ITextTemplatingEngineHost host, StringBuilder template)
            : base(host, template) {
            var hostServiceProvider = (IServiceProvider) host;
            if (hostServiceProvider == null)
                throw new ArgumentNullException("Could not obtain IServiceProvider");
            dte = (EnvDTE.DTE) hostServiceProvider.GetService(typeof(EnvDTE.DTE));
            if (dte == null)
                throw new ArgumentNullException("Could not obtain DTE from host");
            templateProjectItem = dte.Solution.FindProjectItem(host.TemplateFile);
            checkOutAction = (String fileName) => dte.SourceControl.CheckOutItem(fileName);
            projectSyncAction = (IEnumerable<String> keepFileNames) => ProjectSync(templateProjectItem, keepFileNames);

        private static void ProjectSync(EnvDTE.ProjectItem templateProjectItem, IEnumerable<String> keepFileNames) {
            var keepFileNameSet = new HashSet<String>(keepFileNames);
            var projectFiles = new Dictionary<String, EnvDTE.ProjectItem>();
            var originalFilePrefix = Path.GetFileNameWithoutExtension(templateProjectItem.get_FileNames(0)) + ".";
            foreach(EnvDTE.ProjectItem projectItem in templateProjectItem.ProjectItems)
                projectFiles.Add(projectItem.get_FileNames(0), projectItem);

            // Remove unused items from the project
            foreach(var pair in projectFiles)
                if (!keepFileNames.Contains(pair.Key) && !(Path.GetFileNameWithoutExtension(pair.Key) + ".").StartsWith(originalFilePrefix))

            // Add missing files to the project
            foreach(String fileName in keepFileNameSet)
                if (!projectFiles.ContainsKey(fileName))

        private void CheckoutFileIfRequired(String fileName) {
            var sc = dte.SourceControl;
            if (sc != null && sc.IsItemUnderSCC(fileName) && !sc.IsItemCheckedOut(fileName))
                checkOutAction.EndInvoke(checkOutAction.BeginInvoke(fileName, null, null));
} #>


LINQ to SQL cheat sheet

Thumbnail of the LINQ to SQL Cheat Sheet PDF

A few short words to say I’ve put together a cheat sheet for LINQ to SQL with one page for C# and another for VB.NET.

It shows the syntax for a number of common query operations, manipulations and attributes and can be a very useful quick reference :)

Download LINQ to SQL cheat sheet (PDF) (76 KB)


Client-side properties and any remote LINQ provider

David Fowler on the ASP.NET team and I have been bouncing ideas about on how to solve an annoyance using LINQ:

If you write properties on the client you can’t use them in remote LINQ operations.

The problem occurs because these properties can’t be translated and sent to the server as they have been compiled into intermediate language (IL) and not LINQ expression trees that are required for translation by IQueryable implementations. There is nothing available in .NET to let us reverse-engineer the IL back into the methods and syntax that would allow us to translate the intended operation into a remote query.

This means you end up having to write your query in two parts; firstly the part the server can do, a ToList or AsEnumerable call to force that to happen and bring the intermediate results down to the client, and then the operations that can only be evaluated locally. This can hurt performance if you want to reduce or transform the result set significantly.

What we came up (David, Colin Meek and myself) is a provider-independent way of declaring properties just once so they can be used in both scenarios. Computed properties for LINQ to SQL, LINQ to Entities and anything else LINQ enabled with little effort and it works great on .NET 3.5 SP1 :)

Before example

Here we have extended the Employee class to add Age and FullName. We only wanted to people with “da” in their name but we are forced to pull down everything to the client in order to the do the selection.

partial class Employee {
  public string FullName {
    get { return Forename + " " + Surname; }

  public int Age {
    get { return DateTime.Now.Year - BirthDate.Year - (((DateTime.Now.Month < BirthDate.Month)
			|| DateTime.Now.Month == BirthDate.Month && DateTime.Now.Day < BirthDate.Day) ? 1 : 0));

var employees = db.Employees.ToList().Where(e => e.FullName.Contains("da")).GroupBy(e => e.Age);

After example

Here using our approach it all happens server side… and works on both LINQ to Entities and LINQ to SQL.

partial class Employee {
    private static readonly CompiledExpression<Employee,string> fullNameExpression
     = DefaultTranslationOf<Employee>.Property(e => e.FullName).Is(e => e.Forename + " " + e.Surname);
    private static readonly CompiledExpression<Employee,int> ageExpression
     = DefaultTranslationOf<Employee>.Property(e => e.Age).Is(e => DateTime.Now.Year - e.BirthDate.Value.Year - (((DateTime.Now.Month < e.BirthDate.Value.Month) || (DateTime.Now.Month == e.BirthDate.Value.Month && DateTime.Now.Day < e.BirthDate.Value.Day)) ? 1 : 0)));

  public string FullName {
    get { return fullNameExpression.Evaluate(this); }

  public int Age {
    get { return ageExpression.Evaluate(this); }

var employees = db.Employees.Where(e => e.FullName.Contains("da")).GroupBy(e => e.Age).WithTranslations();

Getting started

Usage considerations

The caveats to the usage technique shown above is you need to ensure your class has been initialized before you write queries to it (check out alternatives below) and obviously the expression you register for a property must be able to be translated to the remote store so you will need to constrain yourself to the methods and operators your IQueryable provider supports.

There are a few alternative ways to use this rather than the specific examples above.

Registering the expressions

You can register the properties in the class itself as shown in the examples which means the properties themselves can evaluate the expressions without any reflection calls. Alternatively if performance is less critical you can register them elsewhere and have the methods look up their values dynamically via reflection. e.g.

DefaultTranslationOf<Employee>.Property(e => e.FullName).Is(e => e.Forename + " " + e.Surname);
var employees = db.Employees.Where(e => e.FullName.Contains("da")).GroupBy(e => e.Age).WithTranslations();

partial class Employee {
    public string FullName { get { return DefaultTranslationOf<Employees>.Evaluate<string>(this, MethodInfo.GetCurrentMethod());} }

If performance of the client-side properties is critical then you can always have them as regular get properties with the full code in there at the expense of having the calculation duplicated, once in IL in the property and once as an expression for the translation.

Different maps for different scenarios

Sometimes certain parts of your application may want to run with different translations for different scenarios, performance etc. No problem!

The WithTranslations method normally operates against the default translation map (accessed with DefaultTranslationOf) but there is also another overload that takes a TranslationMap you can build for specific scenarios, e.g.

var myTranslationMap = new TranslationMap();
myTranslationMap.Add<Employees, string>(e => e.Name, e => e.FirstName + " " + e.LastName);
var results = (from e in db.Employees where e.Name.Contains("martin") select e).WithTranslations(myTranslationMap).ToList();

How it works

CompiledExpression<T, TResult>

The first thing we needed to do was get the user-written client-side “computed” properties out of IL and back into expression trees so we could translate them. Given that we also want to evaluate them on the client we need to compile them at run time so CompiledExpression exists which just takes an expression of Func<T, TResult>, compiles it and allows evaluation of objects against the compiled version.


This little class provides both the WithTranslations extensions methods and the internal TranslatingVisitor that unravels the property accesses into their actual registered Func<T, TResult> expressions via the TranslationMap so that the underlying LINQ provider can deal with that instead.


We need to have a map of properties to compiled expressions and for that purpose TranslationMap exists. You can create a TranslationMap by hand and pass it in to WithTranslations if you want to programmatically create them at run-time or have different ones for different scenarios but generally you will want to use…


This helper class lets you register properties against the default TranslationMap we use when nothing is passed to WithTranslations. It also allows you to lookup what is already registered so you can evaluate to that although there is a small reflection performance penalty for that:

public int Age { get { return DefaultTranslationOf<Employees>.Evaluate<int>(this, MethodInfo.GetCurrentMethod()); } }

Have fun!


LINQ to SQL resources

A quick round-up of some useful LINQ to SQL related resources that are available for developers. I’ve not used everything on this list myself so don’t take this as personal endorsement.


  • Entity Developer Add-in for Visual Studio that provides a replacement designer with code templates. Commercial ($99.95)
  • LLBLGen Pro This ORM templating and design tool has a set of LINQ to SQL templates available for generating C# code including file per entity that can be used in conjunction with their designer. Templates are free but require LLBLGen Pro license (€179-249).
  • L2ST4 My templates use Visual Studio’s built in T4 engine and provide a great starting point to customizing the code generation process. Everything that SQL Metal/LINQ to SQL designer can generate is handled including C# and VB.NET generation and are freely licensed under the MS-PL.
  • PLINQO These templates for Eric Smith’s ever-popular CodeSmith templating environment include a whole host of extra functionality beyond the standard generation including entity clone & detach, enum’s from tables, data annotations, batching, auditing and more. Templates are free but require CodeSmith license ($79-$299).
  • T4 Toolbox Oleg Sych has put together a suite of useful T4 templates including ones for producing LINQ to SQL entities, data contexts as well as SQL scripts for altering the schema to reflect changes. C# only, MS-RL.

Note: While the T4 templating language is built-in to Visual Studio 2008/2010 it does not come with syntax highlighting or IntelliSense. Check out either:

  • Clarius Visual T4 Basic ‘community’ version available for free, commercial ‘pro’ version with IntelliSense, sub-templates, preview, user preferences etc. is $99.
  • Tangible T4 Free version available with limited IntelliSense, commercial ‘pro’ version with UML modeling etc. available for $99.


  • David DeWinter David is a dev in test who recently joined our team and hit the ground running with testing, blogging and helping out on the forums.
  • Roger Jennings Roger over at OakLeaf Systems publishes regular articles and roundups of some of the best .NET data access content from around the web including LINQ to SQL.
  • Scott Guthrie Our Corporate Vice President for the .NET Developer Platform takes a very active role in getting his hands dirty and publishes a series of useful LINQ to SQL articles.
  • Sidar Ok Sidar is a regular forum helper and has written a number of great posts on LINQ to SQL including some good POCO coverage.


  • Devart dotConnect Devart’s dotConnect family are database providers for Oracle, MySQL, Postgres and SQLite that also include LINQ support to enable LINQ to SQL like functionality on other platforms. Some database basic versions are free, professional versions are commercial and vary in price (~$99-$209).
  • Hugati DBML/EDMX Tools Add-in for Visual Studio that provides comparison/update facilities between the database and the DBML as well as standardizing names and generating interfaces. Commercial ($49-$119, free 30 day trial).
  • Hugati LINQ to SQL Profiler Profiling tool to help optimize your LINQ to SQL based applications. Commercial ($49-$119, free 45 day trial).
  • LINQpad This invaluable tool helps you write and visualize your LINQ queries in a test-bench without compilation and includes a version for the .NET 4.0 beta. Free to use, auto-completion add-on available ($19).
  • LINQ to SQL Cheat Sheet PDF download of the most popular query and update syntax for C# and VB.NET.

Official guides

  • Samples The official samples includes a whopping 101 snippets showing how to use many of the features and syntax.
  • Programming Guide Includes steps on how to get started, querying, making changes, debugging and background information.
  • Whitepaper Single document describing the architecture, query capabilities, change tracking and life-cycle, multi-tier entities, external mapping etc.
  • Changes in .NET 4.0 List of the changes made to LINQ to SQL to .NET 4.0 including some possible breaking changes



  • Official MSDN forums Great way to get access to the product team directly as well as knowledgeable and experienced users if you have a question or a problem.
  • Official LINQ to SQL FAQ Coverage is a little thin on the ground but it has some useful tips.
  • StackOverflow’s LINQ to SQL tag StackOverflow has rapidly become a leader in questions and answers for a wide variety of developer topics and covers LINQ to SQL (which the site uses for it’s data access too!)