c# – 具有存储库模式的实体框架插入多对多

我继承了一个使用Entity Framework和Repository Pattern的解决方案.
在这个解决方案中,以前的开发人员忘记实现多对多关系,所以现在我必须这样做.

我不太熟悉EF或模式​​,所以我无法得到我想要实现的工作,即插入多对多关系.
我可以让EF在数据库中创建关系表,但不知何故我无法插入它.

我见过other questions similar to this one,但是没有一个与这里的模式实现完全匹配,然后我对一切都不熟悉,无法绕过它.

有人可以看看代码,看看我错过了什么？ (代码已经简化了一点,这不是实际的学生/课程项目,但我使用的是这些名称,因为它们已在之前的例子中使用过)

这是我的代码.非常简化,没有数千个接口.
这没有例外,运行得很好.
当我在“Main”类中调试和快速监视studentUow时,Students.Courses集合确实包含一个值,但它永远不会保存到数据库中.此外,它只包含一个值,即使它应包含多个课程.

实体类

public class Student { // This class already existed
    public int StudentId { get; protected set; }
    public virtual ICollection<Course> Courses { get; set; } // I added this property
}

public class Course { // This class already existed
    public int CourseId { get; protected set; }
    public virtual ICollection<Student> Students { get; set; } // I added this property
}

知识库

public class StudentRepository {
    protected DbContext DbContext { get; private set; }
    protected DbSet<Student> DbSet { get; private set; }
    public StudentRepository(DbContext dbContext) {
        DbContext = dbContext;
        DbSet = dbContext.Set<Student>();
    }

    public virtual void AddOrUpdate(Student entity) {
        if (Exists(entity)) {
            Update(entity);
        } else {
            Add(entity);
        }
    }

    public virtual void Update(Student entity) {
        var dbEntityEntry = DbContext.Entry(entity);
        if (dbEntityEntry.State == EntityState.Detached) {
            DbSet.Attach(entity);
        }
        dbEntityEntry.State = EntityState.Modified;
    }

    public virtual Student Add(Student entity) {
        var dbEntityEntry = DbContext.Entry(entity);
        if (dbEntityEntry.State != EntityState.Detached) {
            dbEntityEntry.State = EntityState.Added;
        } else {
            return DbSet.Add(entity);
        }
        return null;
    }

    public IQueryable<Student> Queryable() {
        return DbSet;
    }

    public bool Exists(Student entity) {
        var objContext = ((IObjectContextAdapter)DbContext).ObjectContext;
        object existingEntity;
        var exists = objContext.TryGetObjectByKey(GetEntityKey(entity), out existingEntity);
        if (exists) objContext.Detach(existingEntity);

        return exists;
    }

    private EntityKey GetEntityKey(Student entity) {
        var objContext = ((IObjectContextAdapter)DbContext).ObjectContext;
        var objSet = objContext.CreateObjectSet<T>();
        var entityKey = objContext.CreateEntityKey(objSet.EntitySet.Name, entity);
        return entityKey;
    }
}

工作单位

public class StudentUow : UnitOfWork<MyDbContext> {
    public StudentRepository Students { get { return CreateRepository<StudentRepository>(); } }
    public CourseRepository Courses { get { return CreateRepository<CourseRepository>(); } }
}

public class UnitOfWork<TContext> where TContext : System.Data.Entity.DbContext {
    private readonly TContext _dbContext;
    private IRepositoryProvider _repositoryProvider;

    protected UnitOfWork(IRepositoryProvider provider) {
        _repositoryProvider = provider;
    }

    protected TRepository CreateRepository<TRepository>() {
        return _repositoryProvider.Create<TRepository>(_dbContext, "default");
    }

    public void Commit() {
        _dbContext.SaveChanges();
    }
}

[Export(typeof(IUnitOfWorkProvider))]
[PartCreationPolicy(CreationPolicy.Shared)]
public class UnitOfWorkProvider {
    [Import] private IRepositoryProvider _repositoryProvider;

    public StudentUow GetStudentUow() {
        return new StudentUow(_repositoryProvider);
    }
}

[Export(typeof(IRepositoryProvider))]
public class MyRepositoryProvider {
    public MyRepositoryProvider() {
        Register<RepositoryFactory<IProductRepository, StudentRepository>>();
    }

    public TRepository Create<TRepository>(DbContext dbContext, string conntextKey)
    {
        var type = typeof (TRepository);
        if (!_factories.ContainsKey(type))
            throw new UnknownFactoryException(type);

        return (TRepository)_factories[type].Create(dbContext);
    }

    public void Register<TRepositoryFactory>() where TRepositoryFactory : IRepositoryFactory, new()
    {
        var factory = new TRepositoryFactory();
        if (_factories.ContainsKey(factory.Type)) throw new FactoryTypeAlreadyRegisteredException(factory.Type);
        _factories[factory.Type] = factory;
    }
}

“主要”课程

public class MyClass {
    public AddCourse(int studentId, List<int> courses) {
        using (var studentUow = new StudentUow()) {
            foreach (int courseId in courses) {
                Student s = studentUow.Student.Queryable().First(x => x.StudentId == studentId);
                Course c = studentUow.Course.Queryable().First(x => x.CourseId == courseId);
                s.Courses.Add(c);

                studentUow.Student.AddOrUpdate(s);
            }
            studentUow.Commit();
        }
    }
}

如果您遗漏了某些功能,请发表评论,然后我会添加它,或者让您知道它在哪里.

解决方法:

默认情况下,EF不在查询中包含相关实体.为此,您需要在需要时手动包含课程.还有一个问题是,在每次迭代中,您一次又一次地取回学生,因此课程集合丢失了.这应该工作：

using System.Data.Entity;
...
using (var studentUow = new StudentUow()) {
    Student s = studentUow.Student.Queryable().Include(x => x.Courses).First(x => x.StudentId == studentId);
    foreach (int courseId in courses) {
        Course c = studentUow.Course.Queryable().First(x => x.CourseId == courseId);
        s.Courses.Add(c);
        c.Students.Add(s);

        studentUow.Course.Update(c);
    }
    studentUow.Student.Update(s);
    studentUow.Commit();
}

如果可能的话,我强烈建议您重构代码.

标签：c,net,entity-framework,repository-pattern
来源： https://codeday.me/bug/20190708/1400082.html