首次接触仓储的概念来自Eric Evans 的经典著作《领域驱动设计－软件核心复杂性应对之道》，但书中没有具体实现。如何实现仓储模式，在我这几年的使用过程中也积累了一些具体的实施经验。根据项目的大小、可维护性、可扩展性，以及并发我们可以做以下几种设计；
1、项目小，扩展性差
public interface IRepository<T> where T : class,new()
{
/// <summary>
/// 创建对象
/// </summary>
/// <param name="model"></param>
/// <returns></returns>
T Create(T model); /// <summary>
/// 更新对象
/// </summary>
/// <param name="model"></param>
/// <returns></returns>
T Update(T model); /// <summary>
/// 根据对象全局唯一标识检索对象
/// </summary>
/// <param name="guid"></param>
/// <returns></returns>
T Retrieve(Guid guid); /// <summary>
/// 根据条件表达式检索对象
/// </summary>
/// <param name="expression">条件表达式</param>
/// <returns></returns>
/// <exception cref = "ArgumentNullException" > source 为 null</exception>
T Retrieve(Expression<Func<T, bool>> expression); /// <summary>
/// 根据对象全局唯一标识删除对象
/// </summary>
/// <param name="guid">对象全局唯一标识</param>
/// <returns>删除的对象数量</returns>
int Delete(Guid guid); /// <summary>
/// 根据对象全局唯一标识集合删除对象集合
/// </summary>
/// <param name="guids">全局唯一标识集合</param>
/// <returns>删除的对象数量</returns>
int BatchDelete(IList<Guid> guids); List<T> GetAll(); List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total);
}
IRepository接口包含了CRUD操作，如果在业务中还需要扩展，只需在IRepository接口中添加即可。
public class RepositoryImpl<T> : IRepository<T> where T : class, new()
{
protected readonly string ConnectionString; protected RepositoryImpl(ISqlHelp sqlHelp)
{
ConnectionString = sqlHelp.SQLConnectionString();
} public int BatchDelete(IList<Guid> guids)
{
using (var dbcontext = new DbContext(ConnectionString))
{
foreach (var item in guids)
{
var model = dbcontext.Set<T>().Find(item);
dbcontext.Entry(model).State = EntityState.Deleted;
}
return dbcontext.SaveChanges();
}
} public T Create(T model)
{
using (var dbcontext = new DbContext(ConnectionString))
{
dbcontext.Entry(model).State = EntityState.Added;
var createRowCount = dbcontext.SaveChanges();
return createRowCount > ? model : null;
}
} /// <summary>
/// 删除模型
/// </summary>
/// <param name="guid">指定的全局标识</param>
/// <returns>删除数量</returns>
/// <exception cref="ArgumentOutOfRangeException"></exception>
public int Delete(Guid guid)
{
using (var dbcontext = new DbContext(ConnectionString))
{
var model = dbcontext.Set<T>().Find(guid);
if (model == null) throw new ArgumentOutOfRangeException(nameof(guid));
dbcontext.Entry(model).State = EntityState.Deleted;
return dbcontext.SaveChanges();
}
} public List<T> GetAll()
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().Where(q => true).ToList();
}
} public List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total)
{
using (var dbcontext = new DbContext(ConnectionString))
{
total = dbcontext.Set<T>().Where(expression).Count();
switch (sortOrder)
{
case SortOrder.Ascending:
return dbcontext.Set<T>().Where(expression).OrderBy(sortPredicate).Skip(skip).Take(take).ToList(); case SortOrder.Descending:
return dbcontext.Set<T>().Where(expression).OrderByDescending(sortPredicate).Skip(skip).Take(take).ToList(); }
throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
}
} /// <summary>
/// 返回序列中的第一个元素
/// </summary>
/// <param name="expression">查询表达式</param>
/// <returns>T</returns>
/// <exception cref="ArgumentNullException">source 为 null</exception>
public T Retrieve(Expression<Func<T, bool>> expression)
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().FirstOrDefault(expression);
}
} public T Retrieve(Guid guid)
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().Find(guid);
}
} public T Update(T model)
{
using (var dbcontext = new DbContext(ConnectionString))
{
dbcontext.Entry(model).State = EntityState.Modified;
var updateRowAcount = dbcontext.SaveChanges();
return updateRowAcount > ? model : null;
}
}
}
RepositoryImpl为IRepository接口的实现。其中ISqlHelp接口包含获取数据库链接字符串的功能，DbContext为EntityFramework类库。
public sealed class UserServer
{
private readonly IRepository<User> _userRepository; public UserServer(IRepository<User> userRepository)
{
_userRepository = userRepository;
} public void CreateUser()
{
var user = new User();
_userRepository.Create(user);
}
}
这是最简单的仓储使用方式，优点是简单、快速，缺点是扩展性差且违反开放-关闭原则（Open-Close Principle）。但如果项目小且项目生存周期短可选择此模式进行快速搭建。
2、项目大，可扩展性好，不对并发做处理。
因为项目要求高扩展性，每次修改都对IRepository修改也违反软件设计原则。这里IRepository接口不变，但是RepositoryImpl做如下修改：
public class RepositoryImpl<T> : IRepository<T> where T : class, new()
{
protected readonly string ConnectionString; protected RepositoryImpl(ISqlHelp sqlHelp)
{
ConnectionString = sqlHelp.SQLConnectionString();
} public virtual int BatchDelete(IList<Guid> guids)
{
using (var dbcontext = new DbContext(ConnectionString))
{
foreach (var item in guids)
{
var model = dbcontext.Set<T>().Find(item);
dbcontext.Entry(model).State = EntityState.Deleted;
}
return dbcontext.SaveChanges();
}
} public virtual T Create(T model)
{
using (var dbcontext = new DbContext(ConnectionString))
{
dbcontext.Entry(model).State = EntityState.Added;
var createRowCount = dbcontext.SaveChanges();
return createRowCount > ? model : null;
}
} /// <summary>
/// 删除模型
/// </summary>
/// <param name="guid">指定的全局标识</param>
/// <returns>删除数量</returns>
/// <exception cref="ArgumentOutOfRangeException"></exception>
public virtual int Delete(Guid guid)
{
using (var dbcontext = new DbContext(ConnectionString))
{
var model = dbcontext.Set<T>().Find(guid);
if (model == null) throw new ArgumentOutOfRangeException(nameof(guid));
dbcontext.Entry(model).State = EntityState.Deleted;
return dbcontext.SaveChanges();
}
} public virtual List<T> GetAll()
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().Where(q => true).ToList();
}
} public virtual List<T> GetAll(Expression<Func<T, bool>> expression, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take, out int total)
{
using (var dbcontext = new DbContext(ConnectionString))
{
total = dbcontext.Set<T>().Where(expression).Count();
switch (sortOrder)
{
case SortOrder.Ascending:
return dbcontext.Set<T>().Where(expression).OrderBy(sortPredicate).Skip(skip).Take(take).ToList(); case SortOrder.Descending:
return dbcontext.Set<T>().Where(expression).OrderByDescending(sortPredicate).Skip(skip).Take(take).ToList(); }
throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
}
} /// <summary>
/// 返回序列中的第一个元素
/// </summary>
/// <param name="expression">查询表达式</param>
/// <returns>T</returns>
/// <exception cref="ArgumentNullException">source 为 null</exception>
public virtual T Retrieve(Expression<Func<T, bool>> expression)
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().FirstOrDefault(expression);
}
} public virtual T Retrieve(Guid guid)
{
using (var dbcontext = new DbContext(ConnectionString))
{
return dbcontext.Set<T>().Find(guid);
}
} public virtual T Update(T model)
{
using (var dbcontext = new DbContext(ConnectionString))
{
dbcontext.Entry(model).State = EntityState.Modified;
var updateRowAcount = dbcontext.SaveChanges();
return updateRowAcount > ? model : null;
}
}
}
}
即在每个方法实现上加上了virtual关键字使方法可以重载。在示例1中业务使用User对象的仓储方式为IRepository<User>，如果业务需要针对User对象集合做批量修改，这时就必须去修改IRepository和RepositoryImpl，所以这里将添加接口IUserRepository，
/// <summary>
/// 用户仓储接口
/// </summary>
public interface IUserRepository:IRepository<User>
{
/// <summary>
/// 批量修改用户生日
/// </summary>
void BatchUpdateUserBirthday();
}
UserRepositoryImpl实现为
public sealed class UserRepositoryImpl: RepositoryImpl<User>,IUserRepository
{
public UserRepositoryImpl(ISqlHelp sqlHelp) : base(sqlHelp)
{ } public void BatchUpdateUserBirthday()
{
using (var dbcontext = new DbContext(ConnectionString))
{
var usersFromDb = dbcontext.Set<User>().Where(q => q.Name.Equals("zhang"));
foreach (var item in usersFromDb)
{
item.Name = "wang";
dbcontext.Entry(item).State = EntityState.Modified;
}
dbcontext.SaveChanges();
}
}
}
这里不对代码的实现合理性做讨论，只是为了说明仓储模式的设计。
而在业务层中的使用如下：
public sealed class UserServer
{
private readonly IUserRepository _userRepository; public UserServer(IUserRepository userRepository)
{
_userRepository = userRepository;
} public void CreateUser()
{
var user = new User();
_userRepository.Create(user);
} public void BatchUpdateBirthDay()
{
_userRepository.BatchUpdateUserBirthday();
}
此仓储模式在实际使用中稍显复杂，每添加一个实体，需要添加对应的接口和实现两个文件，但是这里的一点复杂度换来代码的高扩展性和维护性是值得的。
3、项目庞大，扩展性高，有并发处理需求
因为项目涉及高并发，采用仓储模式+工作单元模式的设计，使用工作单元的原因是可以提高数据库写操作负载，并且在仓储模式中可以根据不同的数据库链接字符串读不同的库。
对于并发的，可以分为多线程、并行处理、异步编程、响应式编程。（引用：《Concurrency in C# Cookbook》—Author，Stephen Cleary）
在仓储中我会使用异步编程实现并发。
仓储接口如下：
public interface IRepository<T> where T:class,IEntity,new ()
{
/// <summary>
/// 根据条件表达式获取集合
/// </summary>
/// <param name="predicate"></param>
/// <returns></returns>
Task<List<T>> FindByAsync(Expression<Func<T, bool>> predicate); IQueryable<T> FindQueryableByAsync(Expression<Func<T, bool>> predicate); /// <summary>
/// 根据对象全局唯一标识检索对象
/// </summary>
/// <param name="ID"></param>
/// <returns></returns>
Task<T> RetrieveAsync(Guid ID); /// <summary>
/// 根据条件表达式检索对象
/// </summary>
/// <param name="predicate"></param>
/// <returns></returns>
Task<T> RetrieveAsync(Expression<Func<T, bool>> predicate); /// <summary>
/// 获取所有数据
/// </summary>
/// <returns></returns>
Task<List<T>> GetAllAsync(); /// <summary>
/// 获取所有数据
/// </summary>
/// <returns></returns>
List<T> GetAll(); /// <summary>
/// 根据条件表示分页获取数据集合
/// </summary>
/// <param name="predicate">断言表达式</param>
/// <param name="sortPredicate">排序断言</param>
/// <param name="sortOrder">排序方式</param>
/// <param name="skip">跳过序列中指定数量的元素，然后返回剩余的元素</param>
/// <param name="take">从序列的开头返回指定数量的连续元素</param>
/// <returns>item1：数据集合；item2：数据总数</returns>
Task<Tuple<List<T>,int>> GetAllAsync(Expression<Func<T, bool>> predicate, Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take);
}
工作单元接口如下：
/// <summary>
/// Unit Of Work Pattern
/// </summary>
public interface IUnitOfWork : IDisposable
{
DbContext DbContext { get; set; } /// <summary>
/// 提交所有更改
/// </summary>
Task CommitAsync(); #region Methods
/// <summary>
/// 将指定的聚合根标注为“新建”状态。
/// </summary>
/// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
/// <param name="obj">需要标注状态的聚合根。</param>
void RegisterNew<T>(T obj)
where T : class, IEntity;
/// <summary>
/// 将指定的聚合根标注为“更改”状态。
/// </summary>
/// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
/// <param name="obj">需要标注状态的聚合根。</param>
void RegisterModified<T>(T obj)
where T : class;
/// <summary>
/// 将指定的聚合根标注为“删除”状态。
/// </summary>
/// <typeparam name="T">需要标注状态的聚合根类型。</typeparam>
/// <param name="obj">需要标注状态的聚合根。</param>
void RegisterDeleted<T>(T obj)
where T : class;
#endregion
}
仓储实现如下：
public class RepositoryImpl<T> : IRepository<T> where T : class, IEntity, new()
{
protected readonly DbContext Context; protected RepositoryImpl(IContextHelper contextHelper)
{
Context = contextHelper.DbContext;
} public virtual async Task<List<T>> FindByAsync(Expression<Func<T, bool>> predicate)
{
return await Context.Set<T>().Where(predicate).ToListAsync();
} public virtual IQueryable<T> FindQueryableByAsync(Expression<Func<T, bool>> predicate)
{
return Context.Set<T>().Where(predicate);
} public virtual async Task<List<T>> GetAllAsync()
{
return await Context.Set<T>().ToListAsync();
} public List<T> GetAll()
{
return Context.Set<T>().ToList();
} public virtual async Task<Tuple<List<T>, int>> GetAllAsync(Expression<Func<T, bool>> predicate,
Expression<Func<T, dynamic>> sortPredicate, SortOrder sortOrder, int skip, int take)
{
var result = Context.Set<T>().Where(predicate);
var total = result.Count();
switch (sortOrder)
{ case SortOrder.Ascending:
var resultAscPaged = await
Context.Set<T>().Where(predicate).OrderBy(sortPredicate).Skip(skip).Take(take).ToListAsync();
return new Tuple<List<T>, int>(resultAscPaged, total); case SortOrder.Descending:
var resultDescPaged = await
Context.Set<T>().Where(predicate)
.OrderByDescending(sortPredicate)
.Skip(skip)
.Take(take).ToListAsync();
return new Tuple<List<T>, int>(resultDescPaged, total);
}
throw new InvalidOperationException("基于分页功能的查询必须指定排序字段和排序顺序。");
} public virtual async Task<T> RetrieveAsync(Expression<Func<T, bool>> predicate)
{
return await Context.Set<T>().FirstOrDefaultAsync(predicate);
} public virtual async Task<T> RetrieveAsync(Guid id)
{
return await Context.Set<T>().FindAsync(id);
}
}
工作单元实现如下：
public class UnitOfWork : IUnitOfWork
{
public DbContext DbContext { get; set; }
public UnitOfWork(IContextHelper contextHelp)
{
DbContext = contextHelp.DbContext;
} /// <summary>
/// Saves all pending changes
/// </summary>
/// <returns>The number of objects in an Added, Modified, or Deleted state</returns>
public virtual async Task CommitAsync()
{
// Save changes with the default options
try
{
await DbContext.SaveChangesAsync();
}
catch (DbUpdateConcurrencyException ex)
{
ex.Entries.Single().Reload();
} } /// <summary>
/// Disposes the current object
/// </summary>
public virtual void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
} /// <summary>
/// Disposes all external resources.
/// </summary>
/// <param name="disposing">The dispose indicator.</param>
private void Dispose(bool disposing)
{
if (!disposing) return;
if (DbContext == null) return; DbContext.Dispose();
DbContext = null;
} public virtual void RegisterNew<TEntity>(TEntity obj) where TEntity : class, IEntity
{
DbContext.Set<TEntity>().Add(obj);
} public virtual void RegisterModified<TEntity>(TEntity obj) where TEntity : class
{
DbContext.Entry(obj).State = EntityState.Modified;
} public virtual void RegisterDeleted<TEntity>(TEntity obj) where TEntity : class
{
DbContext.Entry(obj).State = EntityState.Deleted;
} }
在业务层中的使用同2。