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

public class Customer
{
public string Name { get; set; }
public Address Address { get; set; }
public Address[] Addresses { get; set; }
public List<Address> AddressList { get; set; }
}

public class CustomerDTO
{
public string Name { get; set; }
public AddressDTO Address { get; set; }
public AddressDTO[] Addresses { get; set; }
public List<AddressDTO> AddressList { get; set; }
}

2.2 定义公共方法把Address转化为AddressDTO

/// <summary>
/// 定义转化 Address -> AddressDTO
/// </summary>
/// <returns></returns>
public static Expression<Func<Address, AddressDTO>> CreateAddressDTO()
{
var sourceType = typeof(Address);
var destType = typeof(AddressDTO);
// Address source;
var source = Expression.Parameter(sourceType, "source");
// AddressDTO dest;
var dest = Expression.Parameter(destType, "dest");
var body = Expression.Block(
[dest],
// dest = new AddressDTO();
Expression.Assign(dest, Expression.New(destType)),
// dest.City = source.City;
Expression.Assign(Expression.Property(dest, "City"), Expression.Property(source, "City")),
// return dest;
dest
);
return Expression.Lambda<Func<Address, AddressDTO>>(body, source);
}

2.3 调用公共方法

/// <summary>
/// 定义转化委托 Customer -> CustomerDTO
/// </summary>
/// <returns></returns>
public static Expression<Func<Customer, CustomerDTO>> CreateCustomerDTO()
{
var customerType = typeof(Customer);
var dtoType = typeof(CustomerDTO);
// Customer customer;
var customer = Expression.Parameter(customerType, "customer");
// CustomerDTO dto;
var dto = Expression.Parameter(dtoType, "dto");
// 可以复用的功能方法
var addressDTOConvertFunc = CreateAddressDTO();
var body = Expression.Block(
[dto],
// dto = new AddressDTO();
Expression.Assign(dto, Expression.New(dtoType)),
// dto.Name = customer.Name;
Expression.Assign(Expression.Property(dto, "Name"), Expression.Property(customer, "Name")),
// dto.Address = addressDTOConvertFunc.Invoke(customer.Address);
ConvertAddress(addressDTOConvertFunc, customer, dto),
// dto.Addresses
ConvertAddresses(addressDTOConvertFunc, customer, dto),
// dto.AddressList
ConvertAddressList(addressDTOConvertFunc, customer, dto),
// return dto
dto
);
return Expression.Lambda<Func<Customer, CustomerDTO>>(body, customer);
}

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

var expression = CreateCustomerDTO();
var func = expression.Compile();
Customer _customer = new()
{
Name = "jxj",
Address = new() { City = "gz" },
AddressList = [new() { City = "bj" }],
Addresses = [new() { City = "sh" }]
};
var dto = func(_customer);
// {"Name":"jxj","Address":{"City":"gz"},"Addresses":[{"City":"sh"}],"AddressList":[]}

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

var expression = CreateCustomerDTO();
var func = FastExpressionCompiler.ExpressionCompiler.CompileFast<Func<Customer, CustomerDTO>>(expression);
Customer _customer = new()
{
Name = "jxj",
Address = new() { City = "gz" },
AddressList = [new() { City = "bj" }],
Addresses = [new() { City = "sh" }]
};
var dto = func(_customer);
// {"Name":"jxj","Address":{"City":"gz"},"Addresses":[{"City":"sh"}],"AddressList":[{"City":"bj"}]}

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