Archive for .NET category
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 behaviour
- 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.
Improvements
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-in’s that might be triggered by the changes.
Usage
Initialization
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(); #>Process
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
<#@ 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)
return;
CurrentBlock.Length = template.Length - CurrentBlock.Start;
if (CurrentBlock != header && CurrentBlock != footer)
files.Add(CurrentBlock);
currentBlock = null;
}
public virtual void Process(bool split) {
if (split) {
EndBlock();
String headerText = template.ToString(header.Start, header.Length);
String footerText = template.ToString(footer.Start, footer.Length);
String outputPath = Path.GetDirectoryName(host.TemplateFile);
files.Reverse();
foreach(Block block in files) {
String fileName = Path.Combine(outputPath, block.Name);
String content = headerText + template.ToString(block.Start, block.Length) + footerText;
generatedFileNames.Add(fileName);
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) {
this.host = host;
this.template = template;
}
private Block CurrentBlock {
get { return currentBlock; }
set {
if (CurrentBlock != null)
EndBlock();
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)
return;
base.Process(split);
projectSyncAction.EndInvoke(projectSyncAction.BeginInvoke(generatedFileNames, null, null));
}
protected override void CreateFile(String fileName, String content) {
if (IsFileContentDifferent(fileName, content)) {
CheckoutFileIfRequired(fileName);
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))
pair.Value.Delete();
// Add missing files to the project
foreach(String fileName in keepFileNameSet)
if (!projectFiles.ContainsKey(fileName))
templateProjectItem.ProjectItems.AddFromFile(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));
}
}
} #>[)amien
When an object-relational mapper is too much, DataReader too little
I fired up Visual Studio this evening to write a proof-of-concept app and found myself wanting strongly typed domain objects from a database but without the overhead of an object-relational mapper (the application is read-only).
One solution is to write methods by hand, another is to code generate them but it would be nice to be able to do:
var customers = new SqlCommand("SELECT ID, Name FROM Customer", connection)
.As(r => new Customer { CustomerID = r.GetInt32(0), Name = r.GetString(1) }).ToList();So for any DbCommand object you can turn it into a bunch of classes by specifying the new pattern.
The tiny helper class to achieve this is:
public static class DataHelpers {
public static List<T> ToList<T>(this IEnumerable<T> enumerable) {
return new List<T>(enumerable);
}
public static IEnumerable<T> As<T>(this DbCommand command, Func<IDataRecord, T> map) {
using (var reader = command.ExecuteReader())
while (reader.Read())
yield return map(reader);
}
}It might even be possible to do some cool caching/materialization. I should look into that :)
[)amien
LINQ to SQL cheat sheet
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)
[)amien
Dictionary<T> look-up or create made simpler
The design of a Dictionary<T> lends itself well to a caching or identification mechanism and as a result you often see code that looks like this:
private static Dictionary<string,Employee> employees;
…
public static Employee GetByName(string name) {
Employee employee;
if (!employees.TryGetValue(name, out employee)) {
employee = new Employee(whatever);
employees.Add(name, employee);
}
return employee;
}It’s not that it is particularly difficult but it can be a bit error prone and when you’re doing it over and over. What would be nicer is something that let you do:
public static Employee GetByName(string name) {
return employees.GetOrAdd(name, () => new Employee(whatever));
}Here’s an extension method to drop-in to a static class of your choosing that achieves just that.
public static TDictionaryValue GetOrAdd<TKey, TDictionaryValue>(this IDictionary<TKey, TDictionaryValue> dictionary, TKey key, Func<TDictionaryValue> newValue)
{
TDictionaryValue value;
if (!dictionary.TryGetValue(key, out value)) {
value = newValue.Invoke();
dictionary.Add(key, value);
}
return value;
}[)amien
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.Now.Month
|| DateTime.Now.Month == BirthDate.Now.Month && DateTime.Now.Day < BirthDate.Now.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
Check out this download which includes the necessary project to drop-in to your solution. The caveat to the usage technique shown above is you need to ensure your class has been initialized before you write queries to it. If this is a problem check out the usage considerations section below.
The other major caveat is 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.
Usage considerations
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();Not specifying WithTranslation everywhere
If you are happy to always have the default translation applied simply add the following statement to the top of your file which will bring in a bunch of extensions methods for the usual LINQ query operators that already apply WithTranslation for you :)
using Microsoft.Linq.Translations.Auto;With .NET 4.0
You should be able to drop the ExpressionVisitor class in the download and reference the built-in one.
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.
ExpressiveExtensions
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.
TranslationMap
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 runtime or have different ones for different scenarios but generally you will want to use…
DefaultTranslationOf
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()); } }AutoTranslation
Remembering to specify WithTranslations everywhere can be a pain so if you always want to go via translation and use the default TranslationMap you can include the Microsoft.Linq.Translations.Auto namespace in your code which includes extension methods for all the regular LINQ operations that saves you having to remember.
Have fun!
[)amien