C# .NET源生成器如何处理Attribute

博客园 - xiangji

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xiangji · 2026-08-13 · via 博客园 - xiangji

前言

1. Attribute很重要

作为元数据描述

作为编译参数,影响编译结果

运行是通过反射读取,影响运行结果

作为源生成器触发条件或参数,影响生成的代码

2. SyntaxTree和ISymbol

本文探讨基于SyntaxTree和ISymbol处理Attribute

字符串拼接也可以实现,但不在本文讨论范围

一、Attribute解析

1. AttributeSyntax

AttributeSyntax是Attribute在SyntaxTree中的表现形式

1.1 SyntaxTree中能包含Attribute的对象

MemberDeclarationSyntax及其子类(TypeDeclarationSyntax、FieldDeclarationSyntax、PropertyDeclarationSyntax和MethodDeclarationSyntax等)

ParameterSyntax

1.2 获取AttributeSyntax的方法

首先遍历Attribute的对象的属性AttributeLists获取AttributeListSyntax

再遍历AttributeListSyntax的属性Attributes

var source = @"public class Product
    {
        [Key, Unique]
        public int ProductId { get; set; }
        [Unique]
        [StringLength(100, MinimumLength = 6)]
        public string ProductName { get; set; }
    }";
var syntaxTree = CSharpSyntaxTree.ParseText(source);
var properties = syntaxTree.GetRoot().DescendantNodes().OfType<PropertyDeclarationSyntax>();
foreach (var property in properties)
{
    var attributeLists = property.AttributeLists;
    foreach (var attributeList in attributeLists)
    {
        var attributes = attributeList.Attributes;
        foreach (AttributeSyntax attribute in attributes)
        {
            var name = attribute.Name.ToFullString();
            Assert.NotEmpty(name);
        }
        Assert.True(attributes.Any());
    }
    Assert.True(attributeLists.Any());
}

1.3 获取Attributes效果截图

2. AttributeData

AttributeData是Attribute在ISymbol中的表现形式

2.1 获取AttributeData的方法

通过ISymbol.GetAttributes方法获取AttributeData

var source = @"public class Product
    {
        [Key, Unique]
        public int ProductId { get; set; }
        [Unique]
        [StringLength(100, MinimumLength = 6)]
        public string ProductName { get; set; }
    }";
var driver = SyntaxTreeDriver.CreateDefaultDriver();
var compilation = driver.Compile(source);
var productType = compilation.GetTypeByMetadataName("Product");
Assert.NotNull(productType);
var properties = SymbolReflection.GetProperties(productType);
foreach (var property in properties)
{
    var attributes = property.GetAttributes();
    foreach (AttributeData attribute in attributes)
    {
        var name = attribute.AttributeClass!.Name;
        Assert.NotEmpty(name);
    }
    Assert.True(attributes.Any());
}

2.2 获取GetAttributes效果截图

3. 解析AttributeData

要把AttributeData转化为AttributeSyntax需要先解析AttributeData

3.1 AttributeData由类型和参数构成

类型：AttributeClass

构造函数参数：ConstructorArguments

命名参数：NamedArguments

class AttributeData
{
    INamedTypeSymbol? AttributeClass { get; }
    ImmutableArray<TypedConstant> ConstructorArguments { get; }
    ImmutableArray<KeyValuePair<string, TypedConstant>> NamedArguments { get; }
}

3.2 获取TypedConstant

通过SymbolAttributeHelper.GetArgumentConstant方法获取ConstructorArguments

通过SymbolAttributeHelper.GetArgumentConstant方法重载获取NamedArguments

string sourceCode = @"
    using System;
    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.All, AllowMultiple = true)]
    public class MyAttribute : Attribute;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.MyAttribute");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var validOn = SymbolAttributeHelper.GetArgumentConstant(attribute, 0);
Assert.NotNull(validOn);
var allowMultiple = SymbolAttributeHelper.GetArgumentConstant(attribute, "AllowMultiple");
Assert.NotNull(allowMultiple);

3.3 解析TypedConstant

TypedConstant由Kind、Type和Value(Values)组成

其中Kind有5种(Error、Primitive、Enum、Type和Array等)

其中Values只有当Kind为Array时才可用

class TypedConstant
{
    TypedConstantKind Kind { get; }
    ITypeSymbol? Type { get; }
    object? Value { get; }
    ImmutableArray<TypedConstant> Values { get; }
}

3.4 把TypedConstant转化为Type

通过GetTypeSymbol把TypedConstant转化为INamedTypeSymbol

只适用Kind为Type

特别注意,源代码中类型是Type,符号获取时转化为INamedTypeSymbol,无法直接获取Type

在源生成器是使用ITypeSymbol(及其子接口)来反射并不直接使用Type

var sourceCode = @"
    using System;
    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Class)]
    public class MapAttribute(Type from) : Attribute
    {
        public Type From { get; } = from;
    }
    public record Product(int Id, string Name);
    [Map(typeof(Product))]
    public record ProductDto(int ProductId, string ProductName);
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.ProductDto");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var constant = SymbolAttributeHelper.GetArgumentConstant(attribute, 0);
Assert.NotNull(constant);
INamedTypeSymbol attributeType = constant.Value.GetTypeSymbol();
Assert.NotNull(attributeType);

3.5 把TypedConstant转化为枚举

通过GetEnum把TypedConstant转化为枚举

只适用Kind为Enum

var sourceCode = @"
    using System;

    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.All)]
    public class MyAttribute : Attribute;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.MyAttribute");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var validOn = SymbolAttributeHelper.GetArgumentConstant(attribute, 0);
Assert.NotNull(validOn);
var targets = validOn.Value.GetEnum<AttributeTargets>();
Assert.Equal(AttributeTargets.All, targets);

3.6 把TypedConstant转化为常量原始值

通过GetPrimitive把TypedConstant转化为常量原始值

只适用Kind为Primitive

var sourceCode = @"
    using System;
    using System.ComponentModel.DataAnnotations.Schema;

    namespace ExampleNamespace;

    [Table(""Products"")]
    public record Product(int ProductId, string ProductName);
    ";
var compilation = SyntaxTreeDriver.CreateDefaultDriver()
    .Reference<TableAttribute>()
    .Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.Product");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var constant = SymbolAttributeHelper.GetArgumentConstant(attribute, 0);
Assert.NotNull(constant);
var value = constant.Value.GetPrimitive<string>();
Assert.Equal("Products", value);

3.7 把TypedConstant转化为数组

通过GetValues把TypedConstant转化为数组

只适用Kind为Array

var sourceCode = @"
    using System;
    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Class)]
    public class RecognizeAttribute : Attribute
    {
        public string[] Rules { get; set; } = [];
    }
    public record Product(int Id, string Name);
    [Recognize(Rules = [""Id:ProductId"", ""Name:ProductName""])]
    public record ProductDto(int ProductId, string ProductName);
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.ProductDto");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var constant = SymbolAttributeHelper.GetArgumentConstant(attribute, "Rules");
Assert.NotNull(constant);
var values = constant.Value.GetValues<string>();
Assert.Equal(["Id:ProductId", "Name:ProductName"], values);

3.7 把TypedConstant转化为配置值

通过GetValue把TypedConstant转化为配置值

GetValue可以代替前面四种方法

如果能确定Kind类型还是建议使用对应的专职方法

GetValue实际封装了前面4个方法,按Kind类型调用,性能会有损耗

var sourceCode = @"
    using System;
    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.All)]
    public class MyAttribute : Attribute;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var type = compilation.GetTypeByMetadataName("ExampleNamespace.MyAttribute");
Assert.NotNull(type);
var attribute = type.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var constant = SymbolAttributeHelper.GetArgumentConstant(attribute, 0);
Assert.NotNull(constant);
var value = constant.Value.GetValue<AttributeTargets>();
Assert.Equal(AttributeTargets.All, value);

3.8 泛型Attribute类型参数

通过AttributeClass获取Attribute实际类型

通过TypeArguments获取泛型参数

var sourceCode = @"
    using System;

    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
    public class MapAttribute<TFrom> : Attribute
    {
        public Type From { get; } = typeof(TFrom);
    }
    public readonly record struct User(string Name);
    [Map<User>]
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var syntaxTree = compilation.SyntaxTrees.FirstOrDefault();
Assert.NotNull(syntaxTree);
var classDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<ClassDeclarationSyntax>().LastOrDefault();
Assert.NotNull(classDeclaration);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var symbol = semanticModel.GetDeclaredSymbol(classDeclaration);
Assert.NotNull(symbol);
var attributeData = symbol.GetAttributes().FirstOrDefault();
Assert.NotNull(attributeData);
var attributeClass = attributeData.AttributeClass;
Assert.NotNull(attributeClass);
var attributeTypeArgument = attributeClass.TypeArguments.FirstOrDefault();
Assert.NotNull(attributeTypeArgument);

4 判断是否包含指定Attribute

判断Attribute,存在是触发源生成器或其他逻辑的常用方式

4.1 判断非泛型Attribute

通过GetTypeByMetadataName获取指定的Attribute类型

通过Equals判断类型是否一致

var sourceCode = @"
    using System;

    namespace ExampleNamespace;

    [MyAttribute]
    public class MyClass;
    [AttributeUsage(AttributeTargets.All, AllowMultiple = true)]
    public class MyAttribute : Attribute;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var attributeSymbol = compilation.GetTypeByMetadataName("ExampleNamespace.MyAttribute");
Assert.NotNull(attributeSymbol);
var syntaxTree = compilation.SyntaxTrees.FirstOrDefault();
Assert.NotNull(syntaxTree);
var classDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<ClassDeclarationSyntax>().FirstOrDefault();
Assert.NotNull(classDeclaration);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var symbol = semanticModel.GetDeclaredSymbol(classDeclaration);
Assert.NotNull(symbol);
var attributeData = symbol.GetAttributes().FirstOrDefault();
Assert.NotNull(attributeData);
Assert.True(attributeSymbol.Equals(attributeData.AttributeClass, SymbolEqualityComparer.Default));

4.2 判断泛型Attribute

通过GetTypeByMetadataName获取指定的Attribute类型也支持泛型

通过扩展方法IsGenericType判断是否为泛型

var sourceCode = @"
    using System;

    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
    public class MapAttribute<TFrom> : Attribute
    {
        public Type From { get; } = typeof(TFrom);
    }
    public readonly record struct User(string Name);
    [Map<User>]
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var attributeSymbol = compilation.GetTypeByMetadataName("ExampleNamespace.MapAttribute`1");
Assert.NotNull(attributeSymbol);
var syntaxTree = compilation.SyntaxTrees.FirstOrDefault();
Assert.NotNull(syntaxTree);
var classDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<ClassDeclarationSyntax>().LastOrDefault();
Assert.NotNull(classDeclaration);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var symbol = semanticModel.GetDeclaredSymbol(classDeclaration);
Assert.NotNull(symbol);
var attributeData = symbol.GetAttributes().FirstOrDefault();
Assert.NotNull(attributeData);
var attributeClass = attributeData.AttributeClass;
Assert.NotNull(attributeClass);
Assert.True(attributeClass.IsGenericType(attributeSymbol));

4.3 Attribute通用判断

通过GetTypeByMetadataName获取指定的泛型Attribute

通过SymbolAttributeHelper.GetAttributesByType方法获取Attribute支持泛型

var sourceCode = @"
    using System;

    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
    public class MapAttribute(Type from) : Attribute
    {
        public Type From { get; } = from;
    }
    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
    public class MapAttribute<TFrom> : Attribute
    {
        public Type From { get; } = typeof(TFrom);
    }
    public readonly record struct User(string Name);
    [Map<User>]
    [Map(typeof(User))]
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var attributeSymbol = compilation.GetTypeByMetadataName("ExampleNamespace.MapAttribute");
Assert.NotNull(attributeSymbol);
var attributeGenericSymbol = compilation.GetTypeByMetadataName("ExampleNamespace.MapAttribute`1");
Assert.NotNull(attributeGenericSymbol);
var syntaxTree = compilation.SyntaxTrees.FirstOrDefault();
Assert.NotNull(syntaxTree);
var classDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<ClassDeclarationSyntax>().LastOrDefault();
Assert.NotNull(classDeclaration);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var symbol = semanticModel.GetDeclaredSymbol(classDeclaration);
Assert.NotNull(symbol);
var attributeData = SymbolAttributeHelper.GetAttributesByType(symbol, attributeSymbol)
    .FirstOrDefault();
Assert.NotNull(attributeData);
var attributeGenericData = SymbolAttributeHelper.GetAttributesByType(symbol, attributeGenericSymbol)
    .FirstOrDefault();
Assert.NotNull(attributeGenericData);

二、生成Attribute

1. 生成AttributeSyntax

通过方法SyntaxFactory.Attribute构造AttributeSyntax

1.1 无参的Attribute

var attribute = SyntaxFactory.Attribute(SyntaxFactory.IdentifierName("Fact"));
var code = attribute.ToFullString();
Assert.Equal("Fact", code);

1.2 使用构造函数参数

通过SyntaxFactory.AttributeArgument方法构造Attribute的参数

var attributeName = SyntaxFactory.IdentifierName("InlineData");
var argument = SyntaxFactory.AttributeArgument(SyntaxGenerator.Literal(1));
var attribute = attributeName.Attribute([argument]);
var code = attribute.ToFullString();
Assert.Equal("InlineData(1)", code);

1.3 使用命名参数

使用ToAttributeArgument扩展方法构造Attribute的参数

使用ToAttributeArgument扩展方法重载构造Attribute的命名参数

var attributeName = SyntaxFactory.IdentifierName("AttributeUsage");
var targets = SyntaxFactory.IdentifierName("AttributeTargets").
    Access("Method");
var inherited = SyntaxGenerator.FalseLiteral;
var attribute = attributeName.Attribute([
    targets.ToAttributeArgument(), 
    inherited.ToAttributeArgument("Inherited")]);
var code = attribute.NormalizeWhitespace().ToFullString();
Assert.Equal("AttributeUsage(AttributeTargets.Method, Inherited = false)", code);

2. 把AttributeSyntax附加到SyntaxTree

使用ToSingletonList把AttributeSyntax转化为独立的AttributeListSyntax

还可以用SyntaxFactory.AttributeList合并多个AttributeListSyntax

使用AddAttributeLists方法附加AttributeSyntax

var attribute = SyntaxFactory.IdentifierName("Fact").Attribute();
var method = SyntaxGenerator.VoidType.Method("Simple")
    .WithBody(SyntaxFactory.Block())
    .AddAttributeLists(attribute.ToSingletonList());
var code = method.NormalizeWhitespace().ToFullString();
Assert.Contains("[Fact]", code);

3. 判断AttributeData是否适合当前节点

该场景是把ISymbol的AttributeData附加到SyntaxTree之前先验证是否适用

由于Attribute有ValidOn属性,不符合编译会报错

3.1 只判断AttributeTargets

AttributeSymbolCacher用于缓存Attribute的类型信息,避免相同类型重复解析

以下示例为由结构体User生成类UserDTO,尝试把MyAttribute复制过去

通过VerifyTarget验证原Attribute是否能用于类UserDTO

由于MyAttribute只能用于结构体,所以MyAttribute无法复制到UserDTO

var sourceCode = @"
    using System;

    [AttributeUsage(AttributeTargets.Struct)]
    public class MyAttribute : Attribute;
    [MyAttribute]
    public readonly record struct User(string Name);
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var sourceType = compilation.GetTypeByMetadataName("User");
Assert.NotNull(sourceType);
var attribute = sourceType.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var destType = compilation.GetTypeByMetadataName("UserDTO");
Assert.NotNull(destType);
var attributeCacher = new AttributeSymbolCacher(compilation);
Assert.False(attributeCacher.VerifyTarget(AttributeTargets.Class, attribute));

3.2 判断AttributeTarget及与目标是否冲突

AttributeSymbolCacher用于缓存Attribute的类型信息,避免相同类型重复解析

以下示例为由结构体User生成类UserDTO,尝试把MyAttribute复制过去

通过Verify验证原Attribute是否能用于类UserDTO及是否冲突

虽然MyAttribute也可用于类,但UserDTO已经有一个MyAttribute,所以还是无法复制到UserDTO

Verify还有属性、字段、函数和参数的重载,这些都类似,就不重复举例了

var sourceCode = @"
    using System;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class, AllowMultiple = false))]
    public class MyAttribute : Attribute;
    [MyAttribute]
    public readonly record struct User(string Name);
    [MyAttribute]
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var sourceType = compilation.GetTypeByMetadataName("User");
Assert.NotNull(sourceType);
var attribute = sourceType.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
var destType = compilation.GetTypeByMetadataName("UserDTO");
Assert.NotNull(destType);
var attributeCacher = new AttributeSymbolCacher(compilation);
Assert.False(attributeCacher.Verify(destType, attribute));

4. 把AttributeData转化为AttributeSyntax

通过ToSyntax扩展方法把AttributeData转化为AttributeSyntax

namespaces是生成AttributeSyntax需要添加的命名空间

如果把生成的AttributeSyntax附加到SyntaxTree,namespaces也需要同步添加

var sourceCode = @"
    using System;
    namespace GenerateCoreTests;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class))]
    public class MyAttribute(int value) : Attribute
    {
        public int Value { get; } = value;
    }
    [My(3)]
    public readonly record struct User(string Name);
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var sourceType = compilation.GetTypeByMetadataName("GenerateCoreTests.User");
Assert.NotNull(sourceType);
AttributeData? attribute = sourceType.GetAttributes().FirstOrDefault();
Assert.NotNull(attribute);
List<string> namespaces = [];
AttributeSyntax attributeSyntax = attribute.ToSyntax(namespaces);
var code = attributeSyntax.ToFullString();
Assert.Equal("My(3)", code);
Assert.Single(namespaces);
Assert.Equal("GenerateCoreTests", namespaces[0]);

5. 演示完整的Attribute操作

5.1 源生成流程的Case

通过GetSemanticModel方法获取模型

通过GetDeclaredSymbol方法解析当前类型符号

通过GetTypeByMetadataName方法获取Attribute泛型

判断当前类型符号是否包含指定Attribute及源类型

通过SymbolReflection.GetConstructors方法获取源类型构造函数

通过源类型构造函数获取源类型参数

获取源类型参数的Attribute并调用ToSyntax扩展方法转化为AttributeSyntax

按源类型参数构造目标类型属性并添加AttributeSyntax

var sourceCode = @"
    using System;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;

    namespace ExampleNamespace;

    [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class)]
    public class MapAttribute<TFrom> : Attribute
    {
        public Type From { get; } = typeof(TFrom);
    }
    public readonly record struct User([StringLength(100)]string Name);
    [Map<User>]
    public partial class UserDTO;
    ";
var compilation = SyntaxTreeDriver.DefaultDriver.Compile(sourceCode);
var syntaxTree = compilation.SyntaxTrees.FirstOrDefault();
Assert.NotNull(syntaxTree);
var classDeclaration = syntaxTree.GetRoot().DescendantNodes().OfType<ClassDeclarationSyntax>().LastOrDefault();
Assert.NotNull(classDeclaration);
var semanticModel = compilation.GetSemanticModel(syntaxTree);
var symbol = semanticModel.GetDeclaredSymbol(classDeclaration);
Assert.NotNull(symbol);
var attributeSymbol = compilation.GetTypeByMetadataName("ExampleNamespace.MapAttribute`1");
Assert.NotNull(attributeSymbol);
var attributeData = SymbolAttributeHelper.GetAttributesByType(symbol, attributeSymbol)
    .FirstOrDefault();
Assert.NotNull(attributeData);
var attributeClass = attributeData.AttributeClass;
Assert.NotNull(attributeClass);
var sourceSymbol = attributeClass.TypeArguments.FirstOrDefault() as INamedTypeSymbol;
Assert.NotNull(sourceSymbol);
var constructor = SymbolReflection.GetConstructors(sourceSymbol)
    .FirstOrDefault();
Assert.NotNull(constructor);
var parameterSymbol = constructor.Parameters.FirstOrDefault();
Assert.NotNull(parameterSymbol);
var attributeCacher = new AttributeSymbolCacher(compilation);
var attribute = attributeCacher.GetAttributes(parameterSymbol, AttributeTargets.Property)
    .FirstOrDefault();
Assert.NotNull(attribute);
var attributeNamespaces = new List<string>();
var attributeSyntax = attribute.ToSyntax(attributeNamespaces);
var attributeNamespace = attributeNamespaces.FirstOrDefault();
Assert.NotNull(attributeNamespace);
var propertyType = parameterSymbol.Type.ToSyntax();
var property = propertyType.GetSetProperty(parameterSymbol.Name)
    .Public()
    .AddAttributeLists(attributeSyntax.ToSingletonList());
var type = SyntaxFactory.ClassDeclaration(classDeclaration.Identifier)
    .WithModifiers(classDeclaration.Modifiers)
    .AddMembers(property);
var @namespace = SyntaxFactory.NamespaceDeclaration(SyntaxFactory.IdentifierName(symbol.ContainingNamespace.Name))
    .AddUsings(SyntaxFactory.UsingDirective(SyntaxFactory.IdentifierName(attributeNamespace)))
    .AddMembers(type);
var code = @namespace.NormalizeWhitespace().ToFullString();
Assert.Contains("[StringLength(100)]", code);

5.2 生成的代码

原类型Name参数的Attribute被完美的复制到目标类Name属性上

namespace ExampleNamespace
{
    using System.ComponentModel.DataAnnotations;

    public partial class UserDTO
    {
        [StringLength(100)]
        public string Name { get; set; }
    }
}

三、实现说明

1. 示例执行说明

以上代码执行依赖开源项目EasySyntax、Hand.GenerateCore和Hand.Generators.SyntaxScripting,nuget包如下

Hand.Generators.EasySyntax --version 0.2.1.4

Hand.GenerateCore --version 0.2.1.6

Hand.Generators.SyntaxScripting --version 0.2.1.4-alpha

2. 示例代码及开源源码

源码托管地址: https://github.com/donetsoftwork/Hand.Generators ，欢迎大家直接查看源码。

gitee同步更新:https://gitee.com/donetsoftwork/hand.-generators

如果大家喜欢请动动您发财的小手手帮忙点一下Star,谢谢！！！

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推荐订阅源

博客园 - xiangji

前言

1. Attribute很重要

2. SyntaxTree和ISymbol

一、Attribute解析

1. AttributeSyntax

1.1 SyntaxTree中能包含Attribute的对象

1.2 获取AttributeSyntax的方法

1.3 获取Attributes效果截图

2. AttributeData

2.1 获取AttributeData的方法

2.2 获取GetAttributes效果截图

3. 解析AttributeData

3.1 AttributeData由类型和参数构成

3.2 获取TypedConstant

3.3 解析TypedConstant

3.4 把TypedConstant转化为Type

3.5 把TypedConstant转化为枚举

3.6 把TypedConstant转化为常量原始值

3.7 把TypedConstant转化为数组

3.7 把TypedConstant转化为配置值

3.8 泛型Attribute类型参数

4 判断是否包含指定Attribute

4.1 判断非泛型Attribute

4.2 判断泛型Attribute

4.3 Attribute通用判断

二、生成Attribute

1. 生成AttributeSyntax

1.1 无参的Attribute

1.2 使用构造函数参数

1.3 使用命名参数

2. 把AttributeSyntax附加到SyntaxTree

3. 判断AttributeData是否适合当前节点

3.1 只判断AttributeTargets

3.2 判断AttributeTarget及与目标是否冲突

4. 把AttributeData转化为AttributeSyntax

5. 演示完整的Attribute操作

5.1 源生成流程的Case

5.2 生成的代码

三、实现说明

1. 示例执行说明

2. 示例代码及开源源码