标签：eager-loading entity-framework-6 c generic-repository
我知道有一个工作单元在抽象(DbContext)之上有一个抽象,并且肯定是一种反模式,或者至少没有必要.
我有以下问题：
我有一个通用的IRepository像这样：
public interface IGenericRepository<TEntity> where TEntity : class
{
IEnumerable<TEntity> Get(
Expression<Func<TEntity, bool>> filter = null,
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
string includeProperties = "");
TEntity GetByID(object id);
void Insert(TEntity entity);
void Delete(object id);
void Delete(TEntity entityToDelete);
void Update(TEntity entityToUpdate);
}
这是此接口的实现：
public class GenericRepository<TEntity> : IGenericRepository<TEntity> where TEntity : class
{
internal GymHelperContext context;
internal DbSet<TEntity> dbSet;
public GenericRepository(GymHelperContext context)
{
this.context = context;
dbSet = context.Set<TEntity>();
}
public virtual IEnumerable<TEntity> Get(
Expression<Func<TEntity, bool>> filter = null,
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
string includeProperties = "")
{
IQueryable<TEntity> query = dbSet;
if (filter != null)
{
query = query.Where(filter);
}
foreach (var includeProperty in includeProperties.Split
(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
{
query = query.Include(includeProperty);
}
if (orderBy != null)
{
return orderBy(query).ToList();
}
else
{
return query.ToList();
}
}
public virtual TEntity GetByID(object id)
{
return dbSet.Find(id);
}
public virtual void Insert(TEntity entity)
{
dbSet.Add(entity);
}
public virtual void Delete(object id)
{
TEntity entityToDelete = dbSet.Find(id);
Delete(entityToDelete);
}
public virtual void Delete(TEntity entityToDelete)
{
if (context.Entry(entityToDelete).State == EntityState.Detached)
{
dbSet.Attach(entityToDelete);
}
dbSet.Remove(entityToDelete);
}
public virtual void Update(TEntity entityToUpdate)
{
dbSet.Attach(entityToUpdate);
context.Entry(entityToUpdate).State = EntityState.Modified;
}
}
我有一个名为Facade的实例,它实例化了Mapper和UnitOfWork,如下所示：
public class MuscleFacade
{
private readonly UnitOfWork _unitOfWork = new UnitOfWork();
private readonly MuscleMapping _muscleMapping = new MuscleMapping();
public MuscleFacade()
{
}
public IEnumerable<MuscleViewModel> GetAllMuscles()
{
var source = _unitOfWork.MuscleRepository
.Get()
.ToList();
var result = source.Select(x => _muscleMapping.MuscleToModel(x));
return result;
}
public GymViewModel GetGymViewModel()
{
GymViewModel gymViewModel = new GymViewModel
{
ListOfMuscles = GetAllMuscles().ToList()
};
return gymViewModel;
}
}
MuscleFacade类是我使用Autofac在控制器上注入的类,我在其构造函数中注入了IMuscleFacade.
现在的事情是,我的MuscleTypeViewModel有一个MuscleViewModel列表,这些模型与对应的Domain类映射,并且在这种特殊情况下,MuscleType有很多Muscle(例如：Arm拥有二头肌,三头肌等),因此我将导航属性放在每个其中的一个,像这样：
public class MuscleType : IEntity
{
public int Id { get; set; }
[StringLength(100)]
public string MuscleTypeName { get; set; }
public ICollection<Muscle> Muscles { get; set; }
}
public class Muscle : IEntity
{
public int Id { get; set; }
[StringLength(100)]
public string MuscleName { get; set; }
public int MuscleTypeId { get; set; }
public MuscleType MuscleType { get; set; }
}
现在让我们再次在Facade中查看GetAllMuscles方法：
public IEnumerable<MuscleViewModel> GetAllMuscles()
{
var source = _unitOfWork.MuscleRepository
.Get()
.ToList();
var result = source.Select(x => _muscleMapping.MuscleToModel(x));
return result;
}
如果我想Eager-Load MuscleType,该如何更改Get()以接收和表达Func而不是字符串呢？
解决方法:
您可以定义一个包含您的包含定义的帮助程序类：
abstract class IncludeDefinition<TEntity>
{
public abstract IQueryable<TEntity> Include(IQueryable<TEntity> entities);
}
class IncludeDefinition<TEntity, TProperty> : IncludeDefinition<TEntity>
{
public IncludeDefinition(Expression<Func<TEntity, TProperty>> includeEx)
{
_includeEx = includeEx;
}
private readonly Expression<Func<TEntity, TProperty>> _includeEx;
public override IQueryable<TEntity> Include(IQueryable<TEntity> entities)
{
return entities.Include(_includeEx);
}
}
然后在您的Get方法中使用IncludeDefinition
public IEnumerable<Muscle> Get(params IncludeDefinition<Muscle>[] includes)
{
IQueryable<Muscle> muscles = ...;
foreach (var item in includes)
{
muscles = item.Include(muscles);
}
return muscles.ToList();
}
并调用方法
_unitOfWork.MuscleRepository
.Get(new IncludeDefinition<Muscle, MuscleType>(m => m.MuscleType));
// Include as many as you wish
_unitOfWork.MuscleRepository
.Get(new IncludeDefinition<Muscle, MuscleType>(m => m.MuscleType),
new IncludeDefinition<Muscle, SomeOtherRelatedEntity>(m => m.SomeOtherProperty));
这里的编辑提供了一种“只是包含”而不是编写复杂语法的方法.
创建一个新接口IQueryRepository,该接口支持不带显式包含和包含的Get,从此接口派生IGenericRepository：
public interface IQueryRepository<TEntity>
where TEntity : class
{
IEnumerable<TEntity> Get(
Expression<Func<TEntity, bool>> filter = null,
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null);
IQueryRepository<TEntity> Include<TProperty>(Expression<Func<TEntity, TProperty>> referenceExpression);
}
public interface IGenericRepository<TEntity> : IQueryRepository<TEntity>
where TEntity : class
{
IEnumerable<TEntity> Get(
Expression<Func<TEntity, bool>> filter = null,
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
params IncludeDefinition<TEntity>[] include);
// other methods like GetByID, Add, Update...
}
更新GenericRepository定义-它使用我最初介绍的IncludeDefinition方法,并在调用Include时返回GenericQueryRepositoryHelper.
public class GenericRepository<TEntity> : IGenericRepository<TEntity> where TEntity : class
{
internal DbSet<TEntity> dbSet;
public IEnumerable<TEntity> Get(Expression<Func<TEntity, bool>> filter = null, Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null)
{
return Get(filter, orderBy, new IncludeDefinition<TEntity>[0]);
}
public IEnumerable<TEntity> Get(Expression<Func<TEntity, bool>> filter = null, Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null, params IncludeDefinition<TEntity>[] includes)
{
IQueryable<TEntity> query = dbSet;
foreach (var item in includes)
{
query = item.Include(query);
}
if (filter != null)
{
query = query.Where(filter);
}
if (orderBy != null)
{
return orderBy(query).ToList();
}
else
{
return query.ToList();
}
}
public IQueryRepository<TEntity> Include<TProperty>(Expression<Func<TEntity, TProperty>> referenceExpression)
{
return new GenericQueryRepositoryHelper<TEntity>(this, new IncludeDefinition<TEntity, TProperty>(referenceExpression));
}
// other methods like GetByID, Add, Update...
}
实现GenericQueryRepositoryHelper来存储包含并在调用Get时应用它们
public class GenericQueryRepositoryHelper<TEntity> : IQueryRepository<TEntity>
where TEntity : class
{
private readonly IList<IncludeDefinition<TEntity>> _includeDefinitions;
private readonly IGenericRepository<TEntity> _repository;
internal GenericQueryRepositoryHelper(IGenericRepository<TEntity> repository, IncludeDefinition<TEntity> includeDefinition)
{
_repository = repository;
_includeDefinitions = new List<IncludeDefinition<TEntity>> { includeDefinition };
}
public IEnumerable<TEntity> Get(Expression<Func<TEntity, bool>> filter = null, Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null)
{
return _repository.Get(filter, orderBy, _includeDefinitions.ToArray());
}
public IQueryRepository<TEntity> Include<TProperty>(Expression<Func<TEntity, TProperty>> referenceExpression)
{
_includeDefinitions.Add(new IncludeDefinition<TEntity, TProperty>(referenceExpression));
return this;
}
}
快乐查询包括：
var repo = new GenericRepository<Muscle>(...);
repo.Include(x => x.MuscleType)
.Include(x => x.MuscleType.Muscles)
.Get(x => x.MuscleName == "Test", x => x.OrderBy(m => m.MuscleName));
标签：eager-loading,entity-framework-6,c,generic-repository 来源： https://codeday.me/bug/20191024/1924524.html
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