微软.net表达式编译居然有bug?

微软.net表达式编译居然有bug?

微软.net表达式编译问题困扰本人很久了,
为此我整理了以下case给大家分享
1. 可行性调研

• 用表达式把一个对象转化为另一个对象
  
• 当一个类含有多个同类型属性时,把相同类型转化提取为公共方法
  
• LambdaExpression可以用来定义复用的公共方法
  
• 一切看起来都很完美,但是居然翻车了！！！
  

2. 示例说明

2.1 Customer多个属性包含Address

对应CustomerDTO多个属性包含AddressDTO

1. public class Customer
2. {
3.     public string Name { get; set; }
4.     public Address Address { get; set; }
5.     public Address[] Addresses { get; set; }
6.     public List AddressList { get; set; }
7. }

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1. public class CustomerDTO
2. {
3.     public string Name { get; set; }
4.     public AddressDTO Address { get; set; }
5.     public AddressDTO[] Addresses { get; set; }
6.     public List AddressList { get; set; }
7. }

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2.2 定义公共方法把Address转化为AddressDTO

1. /// <summary>
2. /// 定义转化 Address -> AddressDTO
3. /// </summary>
4. /// <returns></returns>
5. public static Expression<Func> CreateAddressDTO()
6. {
7.     var sourceType = typeof(Address);
8.     var destType = typeof(AddressDTO);
9.     // Address source;
10.     var source = Expression.Parameter(sourceType, "source");
11.     // AddressDTO dest;
12.     var dest = Expression.Parameter(destType, "dest");
13.     var body = Expression.Block(
14.         [dest],
15.         // dest = new AddressDTO();
16.         Expression.Assign(dest, Expression.New(destType)),
17.         // dest.City = source.City;
18.         Expression.Assign(Expression.Property(dest, "City"), Expression.Property(source, "City")),
19.         // return dest;
20.         dest
21.     );
22.     return Expression.Lambda<Func>(body, source);
23. }

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2.3 调用公共方法

1. /// <summary>
2. /// 定义转化委托 Customer -> CustomerDTO
3. /// </summary>
4. /// <returns></returns>
5. public static Expression<Func<Customer, CustomerDTO>> CreateCustomerDTO()
6. {        
7.     var customerType = typeof(Customer);
8.     var dtoType = typeof(CustomerDTO);
9.     // Customer customer;
10.     var customer = Expression.Parameter(customerType, "customer");
11.     // CustomerDTO dto;
12.     var dto = Expression.Parameter(dtoType, "dto");
13.     // 可以复用的功能方法
14.     var addressDTOConvertFunc = CreateAddressDTO();
15.     var body = Expression.Block(
16.         [dto],
17.         // dto = new AddressDTO();
18.         Expression.Assign(dto, Expression.New(dtoType)),
19.         // dto.Name = customer.Name;
20.         Expression.Assign(Expression.Property(dto, "Name"), Expression.Property(customer, "Name")),
21.         // dto.Address = addressDTOConvertFunc.Invoke(customer.Address);
22.         ConvertAddress(addressDTOConvertFunc, customer, dto),
23.         // dto.Addresses
24.         ConvertAddresses(addressDTOConvertFunc, customer, dto),
25.         // dto.AddressList
26.         ConvertAddressList(addressDTOConvertFunc, customer, dto),
27.         // return dto
28.         dto
29.     );
30.     return Expression.Lambda<Func<Customer, CustomerDTO>>(body, customer);
31. }

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2.3.1 代码解读

• CreateCustomerDTO转化Customer为CustomerDTO
  
• ConvertAddress转化Customer.Address为CustomerDTO.Address调用了CreateAddressDTO
  
• ConvertAddresses转化Customer.Addresses为CustomerDTO.Addresses调用了CreateAddressDTO
  
• ConvertAddressList转化Customer.AddressList为CustomerDTO.AddressList调用了CreateAddressDTO
  
• 以上ConvertAddress、ConvertAddresses和ConvertAddressList本文未提供代码,可以到git仓库下载查看
  
• 以上看上去是不是很完美！！！
  
• 但是马上就要翻车了...
  

2.4 测试一下

1. var expression = CreateCustomerDTO();
2. var func = expression.Compile();
3. Customer _customer = new()
4. {
5.     Name = "jxj",
6.     Address = new() { City = "gz" },
7.     AddressList = [new() { City = "bj" }],
8.     Addresses = [new() { City = "sh" }]
9. };
10. var dto = func(_customer);
11. // {"Name":"jxj","Address":{"City":"gz"},"Addresses":[{"City":"sh"}],"AddressList":[]}

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2.4.1 请大家围观翻车现场

• Address和Addresses转化成功了,但是AddressList转化失败了
  
• 如果说LambdaExpression不能复用,为什么Address和Addresses共用LambdaExpression能成功
  
• 而且如果删掉Addresses属性AddressList就能转化成功
  

2.5 换成FastExpressionCompiler再测试一下

1. var expression = CreateCustomerDTO();
2. var func = FastExpressionCompiler.ExpressionCompiler.CompileFast<Func<Customer, CustomerDTO>>(expression);
3. Customer _customer = new()
4. {
5.     Name = "jxj",
6.     Address = new() { City = "gz" },
7.     AddressList = [new() { City = "bj" }],
8.     Addresses = [new() { City = "sh" }]
9. };
10. var dto = func(_customer);
11. // {"Name":"jxj","Address":{"City":"gz"},"Addresses":[{"City":"sh"}],"AddressList":[{"City":"bj"}]}

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换成FastExpressionCompiler全部成功,这是不是实锤是微软的bug
3. 附两个note对比示例

• expression_fast.dib是微软转化失败示例
  
• expression_fast.dib是FastExpressionCompiler转化成功示例
  
• 大家可以下载本地执行
  
• 用vscode打开就能执行(需要Jupyter Notebook插件)
  

现在很纠结是不是要换方案了,还是要依赖第三方FastExpressionCompiler ...
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