组合两个转换表达式

Question

场景:

一些实体类:

public class BookEntity
{
    public int IdBook { get; set; }
    public string Title { get; set; }
}

public class StudentEntity
{
    public int IdStudent { get; set; }
    public string Name { get; set; }
}

public class LoanEntity
{
    public int IdLoan { get; set; }
    public StudentEntity Student { get; set; }
    public BookEntity Book { get; set; }
}

还有一些数据传输对象类:

public class BookDTO
{
    public int IdBook { get; set; }
    public string Title { get; set; }
}

public class StudentDTO
{
    public int IdStudent { get; set; }
    public string Name { get; set; }
}

public class LoanDTO
{
    public int IdLoan { get; set; }
    public StudentDTO Student { get; set; }
    public BookDTO Book { get; set; }
}

我已经有了这个表达式（在 dto 中转换实体）：

Expression<Func<BookEntity, BookDTO>> pred1 = e => new BookDTO
{
    IdBook = e.IdBook,
    Title = e.Title
};

Expression<Func<StudentEntity, StudentDTO>> pred2 = e => new StudentDTO
{
    IdStudent = e.IdStudent,
    Name = e.Name
};

目标：
现在我想创建一个表达式，将 LoanEntity 转换为 LoanDTO。类似于：

Expression<Func<LoanEntity, LoanDTO>> pred3 = e => new LoanDTO
{
    IdLoan = e.IdLoan,
    Book = new BookDTO
    {
        IdBook = e.Book.IdBook,
        Title = e.Book.Title
    },
    Student = new StudentDTO
    {
        IdStudent = e.Student.IdStudent,
        Name = e.Student.Name
    }
};

问题：

如果您注意到 pred3 表达式是由 pred1 和 pred2 表达式的相同代码组成的。

那么是否可以使用 pred1 和 pred2 创建 pred3 来避免代码重复？

Answer 1

是可能的，但您必须在表达式 pred1 和 pred2 中调用 Compile() 方法来调用它：

Expression<Func<LoanEntity, LoanDTO>> pred3 = e => new LoanDTO
{
    IdLoan = e.IdLoan,
    Book = pred1.Compile()(e.Book),
    Student = pred2.Compile()(e.Student)
};

但您只能使用 Func<,>:

Func<BookEntity, BookDTO> pred1 = e => new BookDTO
{
    IdBook = e.IdBook,
    Title = e.Title
};

Func<StudentEntity, StudentDTO> pred2 = e => new StudentDTO
{
    IdStudent = e.IdStudent,
    Name = e.Name
};

那么，你可以这样使用它：

Func<LoanEntity, LoanDTO> pred3 = e => new LoanDTO
{
    IdLoan = e.IdLoan,
    Book = pred1(e.Book),
    Student = pred2(e.Student)
};

Answer 2

您尝试过使用 Install-Package AutoMapper 吗？它是一个完全解决您问题的库。

var config = new MapperConfiguration(cfg => 
{
  cfg.CreateMap<LoanEntity, LoanDTO>();
  cfg.CreateMap<BookEntity, BookDTO>();
  cfg.CreateMap<StudentEntity, StudentDTO>();
});
var mapper = new ExpressionBuilder(config);

Expression<Func<LoanEntity, LoanDTO>> mappingExpression = mapper.CreateMapExpression<LoanEntity, LoanDTO>();

组合两个转换表达式

Combine two Convert Expressions

.net

c#

linq

expression

entity-framework