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微软.net表达式编译问题困扰本人很久了,

为此整理了以下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