C#动态生成实体类的5种方法详解与实战演示

<#@ template debug="false" hostspecific="true" language="C#" #>
<#@ output extension=".cs" #>
<#
    var className = "DynamicEntity";
    var properties = new Dictionary<string, string> 
    {
        {"Id", "int"},
        {"Name", "string"}
    };
#>
// Auto-generated class
public class <#= className #>
{
<# foreach(var prop in properties) { #>
    public <#= prop.Value #> <#= prop.Key #> { get; set; }
<# } #>
}

var compileUnit = new CodeCompileUnit();
var @namespace = new CodeNamespace("DynamicEntities");
var @class = new CodeTypeDeclaration("Person") { IsClass = true };
 
@class.Members.Add(new CodeMemberField(typeof(int), "_age"));
var property = new CodeMemberProperty()
{
    Name = "Age",
    Type = new CodeTypeReference(typeof(int)),
    Attributes = MemberAttributes.Public
};
property.GetStatements.Add(new CodeMethodReturnStatement(
    new CodeFieldReferenceExpression(null, "_age")));
property.SetStatements.Add(new CodeAssignStatement(
    new CodeFieldReferenceExpression(null, "_age"),
    new CodePropertySetValueReferenceExpression()));
    
@class.Members.Add(property);
var provider = new CSharpCodeProvider();
using var writer = new StringWriter();
provider.GenerateCodeFromCompileUnit(compileUnit, writer, null);
File.WriteAllText("Person.cs", writer.ToString());

var syntaxTree = CSharpSyntaxTree.ParseText(@"
using System;
namespace DynamicEntities
{
    public class Employee
    {
        public string FirstName { get; set; }
        public decimal Salary { get; set; }
    }
}");
 
var compilation = CSharpCompilation.Create("DynamicAssembly")
    .AddReferences(MetadataReference.CreateFromFile(typeof(object).Assembly.Location))
    .AddSyntaxTrees(syntaxTree);
 
using var ms = new MemoryStream();
var result = compilation.Emit(ms);
if (result.Success)
{
    var assembly = Assembly.Load(ms.ToArray());
    dynamic obj = Activator.CreateInstance(assembly.GetType("DynamicEntities.Employee"));
    obj.FirstName = "John";
}

var assemblyName = new AssemblyName("DynamicAssembly");
var assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
var moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
var typeBuilder = moduleBuilder.DefineType("Product", TypeAttributes.Public);
 
// 添加属性
var fieldBuilder = typeBuilder.DefineField("_price", typeof(decimal), FieldAttributes.Private);
var propertyBuilder = typeBuilder.DefineProperty("Price", PropertyAttributes.None, typeof(decimal), null);
 
// 生成get/set方法
var getSetAttr = MethodAttributes.Public | MethodAttributes.SpecialName;
var getMethod = typeBuilder.DefineMethod("get_Price", getSetAttr, typeof(decimal), Type.EmptyTypes);
var getIL = getMethod.GetILGenerator();
getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Ldfld, fieldBuilder);
getIL.Emit(OpCodes.Ret);
 
var setMethod = typeBuilder.DefineMethod("set_Price", getSetAttr, null, new[] { typeof(decimal) });
var setIL = setMethod.GetILGenerator();
setIL.Emit(OpCodes.Ldarg_0);
setIL.Emit(OpCodes.Ldarg_1);
setIL.Emit(OpCodes.Stfld, fieldBuilder);
setIL.Emit(OpCodes.Ret);
 
propertyBuilder.SetGetMethod(getMethod);
propertyBuilder.SetSetMethod(setMethod);
 
var dynamicType = typeBuilder.CreateType();
dynamic obj = Activator.CreateInstance(dynamicType);
obj.Price = 99.99m;