Question

如何设置与此查询的区别

return _dataContext.ProjectPictures.Include("Projects").Include("ProjectPictureTypes").Where(p => p.ProjectPictureTypes.Id == 1).ToList();

我需要像

这样的东西

return _dataContext.ProjectPictures.Include("Projects").Include("ProjectPictureTypes").Where(p => p.ProjectPictureTypes.Id == 1).Distinct(p=>p.Projects.Id).ToList();

Answer 1

假设您在数据库中按照您希望的方式设置了外键关系，并假设您的LINQ-to-SQL类完全反映了这些关系，看起来您想要的东西如下：

DataContext.Projects
    .Where(a => a.ProjectPictures.ProjectPictureType_ID == 1)
    .Distinct()
    .Select(a => a.Project_ID)
    .ToList()

我假设您的数据库结构如下所示：

Projects                      ProjectPictures
========                      ===============
Project_ID (PK, int)          ProjectPicture_ID (PK, int)
                              Project_ID (FK, int)
                              ProjectPictureType_ID (FK, int)

ProjectPictureTypes
===================
ProjectPictureType_ID (PK, int)

Answer 2

据我所知，您希望所有与“ProjectPictureTypes”链接的项目ID为1。

据我所知，你可能想看看分组和合适的聚合 - 不管这是什么。然后p.Projects.Id上的分组对于p.Projects.Id是不同的。困难时期可能是适当的聚合 - 如果在商业逻辑意义上有一个。

HTH

Answer 3

您必须编写自定义IEqualityComparer

public class ProjectPicturesComparer: IEqualityComparer< ProjectPictures >
    {
        // Products are equal if their names and product numbers are equal.
        public bool Equals(ProjectPictures p, ProjectPictures p2)
        {
            return p.Projects.Id == p2.Projects.Id;
        }

        // If Equals() returns true for a pair of objects,
        // GetHashCode must return the same value for these objects.

        public int GetHashCode(ProjectPictures p)
        {
            // Calculate the hash code for the product.
            return  p.Projects.Id.GetHashCode();
        }

    }

然后你会做

return _dataContext.ProjectPictures.Include("Projects").Include("ProjectPictureTypes").Where(p => p.ProjectPictureTypes.Id == 1)..Distinct(new ProjectPicturesComparer()).ToList()

linq鲜明的领域

3 个答案: