如何用IEnumerable<Class>加入List<Class>？

问题描述 投票：0回答：1

我有以下的类，我有一个从数据库中获取数据的服务。

  public class Course 
    {
        public string CourseNumber { get; set; }
        public List<PriceGroup> PriceGroups { get; set; }
    }


   public class PriceGroup
    {
        public int Id { get; set; }
        public string CourseNumber { get; set; }
    }

我有一个从数据库中获取数据的服务。课程是一个 IEnumerable<Course> 而priceGroups是一个 IEnumerable<PriceGroup>. 正如你在课程类中看到的，一个课程有一个 List<PriceGroup>. 我需要以某种方式将每个价格组添加到 IEnumerable<PriceGroup> 列表中的每门课程 IEnumerable<Course> 如果它们在变量上吻合 CourseNumber. 因此，我将最终与一个正确的课程包含正确的。List<PriceGroup>'s

public async Task<IEnumerable<Course>> GetAllAsync()
        {
            //courses is an IEnumerable<Course>
            var courses = await _courseRepository.GetAllAsync();

            //priceGroups is an IEnumerable<PriceGroup>
            var priceGroups = await _coursePriceGroupRepository.GetAllAsync();     

            courses.GroupJoin(priceGroups, c => c.PriceGroups.Select(i => i.CourseNumber), pg => pg.CourseNumber, (c, pg) => new
            {

            });    
            return await courses;
        }

为了做到这一点，我曾尝试过做GroupJoin，但没有成功。我还没有完成这个尝试，因为我在心理上完全卡住了。也许我想做的事情是不可能通过GroupJoin实现的。有谁知道有什么方法可以实现我所需要的？

linq lambda poco
1个回答
1
投票

所以您需要所有（或部分）课程，每个课程都有所有（或部分）价格群。

课程和PriceGroups之间有一个直接的一对多关系。每一门课程都有零个或多个价格群，每个价格群只属于一门课程，即外键CourseNumber所指的课程。

你说的对，只要你想要项目及其子项目，你就用GroupJoin。

public async Task<IEnumerable<Course>> GetAllAsync()
{
    IEnumerable<Course> courses = await _courseRepository.GetAllAsync();
    IEnumerable<PriceGroup> priceGroups = await _coursePriceGroupRepository.GetAllAsync();     

    var queryCoursesWithPriceGroups = courses.GroupJoin( // GroupJoin Courses
        priceGroups,                                     // with PriceGroups
        course => course.CourseNumber,                   // from every Course take primary key
        priceGroup => priceGroup.CourseNumber,           // from every PriceGroup take foreign key
        (course, priceGroupsOfThisCourse) => new        // from every Course with
        {                                               // its priceGroups make one new
             // Select the Course properties you plan to use:
             Id = course.Id,
             Name = course.Name,
             StartDate = course.StartDate,
             ...

             PriceGroups = priceGroupsOfThisCourse.Select(priceGroup => new
             {
                  // Select only the PriceGroup properties that you plan to use
                  Id = priceGroup.Id,
                  Name = priceGroup.Name,
                  ...

                  // not needed, you know the value:
                  // CourseId = priceGroup.CourseId
             })
             .ToList(),
       });
       // Note: this is a query. It is not executed yet!

       return await queryCoursesWithPriceGroups.ToListAsync();
0
投票
//Assuming courseNumber is unique in Courses table
return Courses.Select( c=> { c.PriceGroup=priceGroup.Where(p=>p.CourseNumber==c.CourseNumber).ToList(); return c; });
0
投票

我做了一个实际的例子，很明显，你应该用仓库的方法代替假方法。

class Program
{
    static async void Main(string[] args)
    {
        var courses = GetAllAsync().Result;
    }

    private static async Task<IEnumerable<Course>> GetAllAsync()
    {
        //courses is an IEnumerable<Course>
        var courses = await GetCoursesAsync();

        //priceGroups is an IEnumerable<PriceGroup>
        var priceGroups = await GetPriceGroups();

        foreach (var course in courses)
        {
            foreach (var priceGroup in priceGroups.Where(x => x.CourseNumber == course.CourseNumber))
            {
                course.PriceGroups.Add(priceGroup);
            }
        }

        return courses;
    }

    private static async Task<IEnumerable<Course>> GetCoursesAsync()
    {
        return await Task.FromResult<IEnumerable<Course>>(
            new List<Course>() {
                new Course{
                    CourseNumber = "PIZZA1",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA2",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA3",
                    PriceGroups = new List<PriceGroup>()
                },
            }
        );
    }

    private static async Task<IEnumerable<PriceGroup>> GetPriceGroups()
    {
        return await Task.FromResult<IEnumerable<PriceGroup>>(
            new List<PriceGroup>() {
                new PriceGroup{
                    Id = 1,
                    CourseNumber = "PIZZA1"
                },
                new PriceGroup{
                    Id = 2,
                    CourseNumber = "PIZZA2"
                },
                new PriceGroup{
                    Id = 3,
                    CourseNumber = "PIZZA3"
                }
            }
        );
    }
}

public class Course
{
    public string CourseNumber { get; set; }
    public List<PriceGroup> PriceGroups { get; set; }
}

public class PriceGroup
{
    public int Id { get; set; }
    public string CourseNumber { get; set; }
}

当你从DB中返回数据时，你应该避免使用IEnumerable，你可能会产生意想不到的行为。我建议你用这种方法。

class Program
{
    static void Main(string[] args)
    {
        var courses = GetAllAsync().Result;
    }

    private static async Task<List<Course>> GetAllAsync()
    {
        var courses = await GetCoursesAsync();

        var priceGroups = await GetPriceGroups();

        courses.ForEach(x => { x.PriceGroups.AddRange(priceGroups.Where(y => y.CourseNumber == x.CourseNumber)); });

        return courses;
    }

    private static async Task<List<Course>> GetCoursesAsync()
    {
        return await Task.FromResult(
            new List<Course>() {
                new Course{
                    CourseNumber = "PIZZA1",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA2",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA3",
                    PriceGroups = new List<PriceGroup>()
                },
            }
        );
    }

    private static async Task<List<PriceGroup>> GetPriceGroups()
    {
        return await Task.FromResult(
            new List<PriceGroup>() {
                new PriceGroup{
                    Id = 1,
                    CourseNumber = "PIZZA1"
                },
                new PriceGroup{
                    Id = 2,
                    CourseNumber = "PIZZA2"
                },
                new PriceGroup{
                    Id = 3,
                    CourseNumber = "PIZZA3"
                }
            }
        );
    }
}

public class Course
{
    public string CourseNumber { get; set; }
    public List<PriceGroup> PriceGroups { get; set; }
}

public class PriceGroup
{
    public int Id { get; set; }
    public string CourseNumber { get; set; }
}

我也做了一个使用GroupJoin的版本。

class Program
{
    static void Main(string[] args)
    {
        var courses = GetAllAsync().Result;
    }

    private static async Task<List<Course>> GetAllAsync()
    {
        var courses = await GetCoursesAsync();

        var priceGroups = await GetPriceGroups();

        var groupedData = courses.GroupJoin(priceGroups,
                course => course.CourseNumber,
                priceGroup => priceGroup.CourseNumber,
                (course, priceGroupsCollection) =>
                new
                {
                    CourseNumber = course.CourseNumber,
                    PriceGroups = priceGroupsCollection.ToList()
                });

        courses.ForEach(x => { x.PriceGroups = groupedData.FirstOrDefault(y => y.CourseNumber == x.CourseNumber)?.PriceGroups ?? new List<PriceGroup>(); });

        return courses;
    }

    private static async Task<List<Course>> GetCoursesAsync()
    {
        return await Task.FromResult(
            new List<Course>() {
                new Course{
                    CourseNumber = "PIZZA1",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA2",
                    PriceGroups = new List<PriceGroup>()
                },
                new Course{
                    CourseNumber = "PIZZA3",
                    PriceGroups = new List<PriceGroup>()
                },
            }
        );
    }

    private static async Task<List<PriceGroup>> GetPriceGroups()
    {
        return await Task.FromResult(
            new List<PriceGroup>() {
                new PriceGroup{
                    Id = 1,
                    CourseNumber = "PIZZA1"
                },
                new PriceGroup{
                    Id = 2,
                    CourseNumber = "PIZZA2"
                },
                new PriceGroup{
                    Id = 3,
                    CourseNumber = "PIZZA3"
                },
                new PriceGroup{
                    Id = 4,
                    CourseNumber = "PIZZA1"
                }
            }
        );
    }
}

public class Course
{
    public string CourseNumber { get; set; }
    public List<PriceGroup> PriceGroups { get; set; }
}

public class PriceGroup
{
    public int Id { get; set; }
    public string CourseNumber { get; set; }
}
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