How to create an Immutable Value Object with lots of properties in C #

Question

The task is to define with the least amount of code an immutable ValueObject with a large number of properties.

I use NHibernate as ORM , therefore properties should be virtual and public / protected . This object is mapped to a table from the database.

This object should not change, but it is necessary that it can be created.

If there are not many properties, then there are no problems, like this:

 public class ElectricDevice { public virtual int Id { get; protected set; } public virtual string Name { get; protected set; } public virtual bool IsDecommissioned { get; protected set;} public ElectricDevice(int id, string name, bool isDecommissioned) { Id = id; Name = name; IsDecommissioned = isDecommissioned; } }

But if there are a lot of properties, for example, 20, then it is somehow inconvenient to write a class for a long time (besides, there should be a lot of such classes). It is also not nice to create such an object through the constructor. Any ideas? Maybe in C # 6 any new syntax?

Like ElectricDevice electricDevice = new ElectricDeviceBuilder() { Id = id, Name = name, OtherProperty = otherValue }.Build();
Judging by how you use it, you need code generation, not a handy constructor.

Community spirit ♦ one · Accepted Answer · 2016-01-22T13:46:54

If you need a fluent interface, I got this solution based on the @Stack answer:

We get attribute to mark classes for which you need to build Builder :

 namespace BuildCodegen { class CreateBuilderAttribute : Attribute { } }

Mark this attribute our class:

 [CreateBuilder] public class ElectricDevice { public virtual int Id { get; protected set; } public virtual string Name { get; protected set; } public virtual bool IsDecommissioned { get; protected set; } public ElectricDevice(int id, string name, bool isDecommissioned) { Id = id; Name = name; IsDecommissioned = isDecommissioned; } }

We start a TextTemplate project in our project (it describes in the next answer exactly how this is done), call it Builders.tt .

To access the existing code, CodeModel use CodeModel , rather than reflection, CodeModel reflection has known problems (late updating, blocking of assemblies in memory).

So, put the following code in Builders.tt :

 <# /* hostspecific = true, т. к. мы используем CodeModel Visual Studio */ #> <#@ template debug="false" hostspecific="true" language="C#" #> <#@ assembly name="System.Core" #> <#@ assembly name="System.Data" #> <#@ assembly name="EnvDte" #> <#@ import namespace="System.Linq" #> <#@ import namespace="System.Text" #> <#@ import namespace="System.Collections" #> <#@ import namespace="System.Collections.Generic" #> <#@ import namespace="EnvDTE" #> <#@ output extension=".cs" #> <# // задаём вручную имя атрибута (как сделать лучше?) var attributeFullName = "BuildCodegen.CreateBuilderAttribute"; var visualStudio = (EnvDTE.DTE)((this.Host as IServiceProvider) .GetService(typeof(EnvDTE.DTE))); var project = (EnvDTE.Project)visualStudio.Solution .FindProjectItem(this.Host.TemplateFile).ContainingProject; var codeModel = project.CodeModel; // получили модель кода: var classes = codeModel.CodeElements.Cast<CodeElement>().SelectMany(GetClasses); var classesThatNeedBuilder = classes.Where(c => c.Attributes.Cast<CodeAttribute>() .Any(attr => attr.FullName == attributeFullName)); foreach (var ccl in classesThatNeedBuilder) { var namespaceName = ccl.Namespace.FullName; var className = ccl.Name; var builderName = className + "Builder"; var properties = ccl.Children .OfType<CodeProperty>() .Select(p => new PropertyDescriptor(p)) .ToList(); // Каждый builder кладём в то же пространство имён, что и // производимый им класс. (Это легко переделать, разумеется.) // Также мы предполагаем, что у производимого класса есть // конструктор, принимающий все атрибуты, с именами, соответствующими // именам свойств, но со строчной буквы (если это не так, нужно // поискать конструктор и имена параметров через CodeModel) #> namespace <#= namespaceName #> { public class <#= builderName #> { public <#= className #> Build() { return new <#= className #>(<#= string.Join(", ", properties.Select(p => p.LowerName + ": " + p.LowerName)) #>); } <# foreach (var prop in properties) { // для каждого из свойств определяем несущее поле и // fluent-метод его установки #> <#= prop.Type #> <#= prop.LowerName #>; public <#= builderName #> With<#= prop.UpperName #>(<#= prop.Type #> <#= prop.LowerName #>) { this.<#= prop.LowerName #> = <#= prop.LowerName #>; return this; } <# } #> } } <# } #> <#+ // вспомогательный метод: получаем рекурсивно список классов // мы смотрим только внутри пространств имён, но не внутри других классов // (исключительно из-за лени, ну и нужно для вложенного класса придумать, // куда же класть builder) IEnumerable<CodeClass> GetClasses(CodeElement elt) { CodeClass ccl = elt as CodeClass; if (ccl != null) return new[] { ccl }; CodeNamespace cns = elt as CodeNamespace; if (cns != null) return cns.Members.Cast<CodeElement>().SelectMany(GetClasses); return Enumerable.Empty<CodeClass>(); } // ну и мелкий класс-обёртка для свойства class PropertyDescriptor { public readonly string Type; public readonly string UpperName; public readonly string LowerName; public PropertyDescriptor(CodeProperty property) { this.Type = property.Type.AsString; var name = property.Name; this.UpperName = char.ToUpper(name[0]) + name.Substring(1); this.LowerName = char.ToLower(name[0]) + name.Substring(1); } } #>

We get this automatically generated class:

 namespace BuildCodegen { public class ElectricDeviceBuilder { public ElectricDevice Build() { return new ElectricDevice(id: id, name: name, isDecommissioned: isDecommissioned); } int id; public ElectricDeviceBuilder WithId(int id) { this.id = id; return this; } string name; public ElectricDeviceBuilder WithName(string name) { this.name = name; return this; } bool isDecommissioned; public ElectricDeviceBuilder WithIsDecommissioned(bool isDecommissioned) { this.isDecommissioned = isDecommissioned; return this; } } }

By the way, the Entity-class itself can also be generated automatically.

Answer 2 · 2016-01-21T20:31:36

if there are a lot of properties, for example, 20, then it is somehow inconvenient to write a class

If you need to define a wrapper class for a table from a database with many properties, you can use T4, the code generator in Visual Studio.
To do this, in Visual Studio, press Ctrl + Shift + A, Ctrl + E, type t4, and select Text Template. In the created TextTemplate.tt file specify the following code:

 <#@ template debug="false" hostspecific="false" language="C#" #> <#@ assembly name="System.Core" #> <#@ assembly name="System.Data" #> <#@ import namespace="System.Linq" #> <#@ import namespace="System.Text" #> <#@ import namespace="System.Collections.Generic" #> <#@ output extension=".cs" #> <# var cs = @"Data Source=(localdb)\DB;Initial Catalog=Test;Integrated Security=True;"; var cn = new System.Data.SqlClient.SqlConnection(cs); // тут читаем схему базы дынных и создаем коллекцию имен и типов свойств // ... var ps = new [] { new [] { "p1", "int" }, new [] { "p2", "string" } // ... много других элементов }; #> namespace App { public class Wrapper { <# foreach(var p in ps) { #> public virtual <#= p[1] #> <#= p[0] #> { get; protected set; } <# } #> } }

When you save TextTemplate.tt, TextTemplate.c will be created

  namespace App { public class Wrapper { public virtual int p1 { get; protected set; } public virtual string p2 { get; protected set; } } }

This may make life easier, but it will be as difficult to use this class as before.
What I wanted to hear is ElectricDevice electricDevice = new ElectricDeviceBuilder() { Id = id, Name = name, OtherProperty = otherValue }.Build();
If I do code generation, I know where to look at an example.
PS For such a builder, you can also do code generation, by the way.

Andrey K. Andrey K. 620 four 21 · Answer 3 · 2016-01-22T13:58:58

Just in case, I will write about how you can avoid manually writing many parameters into the constructor. If anything, then criticize.

An object:

 public class RoadDevice { public virtual int Id { get; protected set; } public virtual string Name { get; protected set; } public virtual bool IsDecommissioned { get; protected set;} protected RoadDevice() { } }

Builder:

 //Этот объкт immutable и в перспективе достаточно большой, поэтому для него можно сделать билдер для удобства internal class RoadDeviceBuilder : RoadDevice { public RoadDeviceBuilder() : base() { } public RoadDeviceBuilder WithIdAndName(int id, string name) { this.Id = id; this.Name = name; return this; } public RoadDeviceBuilder WithIsDecomissionedFlag(bool isDecommissioned) { this.IsDecommissioned = isDecommissioned; return this; } public RoadDevice Build() { return this; } }

How to create an Immutable Value Object with lots of properties in C #

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