Fluent LINQ EF Core-选择过滤的子属性

问题描述

我有以下课程：

  public class User
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
    }

    public class ParentEntity
    {
        public Guid Id { get; set; }

        public string SomeProperty { get; set; }

        public ICollection<ChildEntity> ChildEntities { get; set; }

    }

    public class ChildEntity
    {
        public Guid Id { get; set; }

        public int Vote { get; set; }

        public Guid UserId { get; set; }
    }

    public class ReturnedParentDto
    {
        public Guid Id { get; set; }
        public string SomeProperty { get; set; }
        public int Vote { get; set; }

    }

我希望能够返回ParenEntities的完整列表，但是要获取User类的ID（UserClassId），然后过滤ParentUser的ICollection，其中UserUid = UserClassId，因此始终仅返回1 ChildEntity。然后，我想从返回的ChildEntity中提取特定字段，并将其与ParentEntity字段合并。最终结果应类似于ReturnedParentDto。

我想要像这样

ParentEntities.Include(v => v.ChildEntities).ToList()

这在EF Core 5中似乎可行，但我的项目在3.1中。

解决方法

您可以按照以下步骤进行操作

方法1：

var result = result = parentEntities.Include(x => x.ChildEntities.Where(y => y.UserId == userId))
     .Select(x => new ReturnedParentDto {
          Id = x.Id,SomeProperty = x.SomeProperty,Vote = x.ChildEntities.FirstOrDefault()?.Vote // userId is the variable here
     });

方法2：

var result = parentEntities.Select(x => 
  new ReturnedParentDto {
      Id = x.Id,Vote = x.ChildEntities.FirstOrDefault(y => y.UserId == userId)?.Vote // userId is the variable here
 });