我在我的应用程序中设置了一个通用存储库，但我遇到了一些 LINQ 查询的问题。
对于非通用的，这就是我要做的：
private IObjectSet<T> _objectSet;
public List<int?> GetGroups()
{
List<object> objectGroups = new List<object>();
List<int?> intGroups = new List<int?>();
var r = (from n in _objectSet
select n.Group_ID).Distinct();
objectGroups = r.OrderBy(n => n.Value).ToList();
foreach (object value in objectGroups)
{
intGroups.Add((int?)value);
}
return intGroups;
}
由于这是T类型的通用类型，因此在键入“n”时。, IntelliSense 没有列出任何选项，因为n的类型没有明确定义（对吗？）。
所以这是我到目前为止所拥有的：
public interface IRepository<T> : IDisposable where T : class
{
IQueryable<T> Fetch();
IEnumerable<T> GetAll();
IEnumerable<T> GetAll(bool activeOnly);
IEnumerable<T> GetAll(string groupID, bool activeOnly);
IEnumerable<T> Find(Func<T, bool> predicate);
T Single(Func<T, bool> predicate);
T First(Func<T, bool> predicate);
List<int?> GetGroups();
int Add(T entity);
void Delete(T entity);
void Attach(T entity);
void SaveChanges();
void SaveChanges(SaveOptions options);
}
public class DataRepository<T> : IRepository<T> where T : class
{
/// <summary>
/// The context object for the database
/// </summary>
private ObjectContext _context;
private IEnumerable<T> _previousEntries;
private string _PKName;
/// <summary>
/// The IObjectSet that represents the current entity.
/// </summary>
private IObjectSet<T> _objectSet;
public DataRepository()
{
switch (typeof(T).Name)
{
case "CRM_Patient":
_context = new TheseEntities();
_PKName = "key_patient";
break;
case "CRM_Account":
_context = new ThoseEntities();
_PKName = "accountnumber";
break;
case "CRM_Supplier":
_context = new OtherEntities();
_PKName = "supplierid";
break;
default:
_context = new OtherEntities();
break;
}
_objectSet = _context.CreateObjectSet<T>();
_previousEntries = this.GetAll();
}
/// <summary>
/// Gets all records as an IQueryable
/// </summary>
/// <returns>An IQueryable object containing the results of the query</returns>
public IQueryable<T> Fetch()
{
return _objectSet;
}
/// <summary>
/// Gets all records as an IEnumberable
/// </summary>
/// <returns>An IEnumberable object containing the results of the query</returns>
public IEnumerable<T> GetAll()
{
return Fetch().AsEnumerable();
}
/// <summary>
/// Finds a record with the specified criteria
/// </summary>
/// <param name="predicate">Criteria to match on</param>
/// <returns>A collection containing the results of the query</returns>
public IEnumerable<T> Find(Func<T, bool> predicate)
{
return _objectSet.Where<T>(predicate);
}
public List<int?> GetGroups()
{
List<object> objectGroups = new List<object>();
List<int?> intGroups = new List<int?>();
//var r = (from n in _objectSet
// select n.GetType().GetProperty("Group_ID").GetValue(n, null)).Distinct();
var r = Fetch().Select(n => n.GetType().GetProperty("Group_ID").GetValue(n, null)).Distinct();
objectGroups = r.OrderBy(n => n.GetType().GetProperty("Value").GetValue(n, null)).ToList();
foreach (object value in r)
{
intGroups.Add((int?)value);
}
return intGroups;
}
/// <summary>
/// Gets a single record by the specified criteria (usually the unique identifier)
/// </summary>
/// <param name="predicate">Criteria to match on</param>
/// <returns>A single record that matches the specified criteria</returns>
public T Single(Func<T, bool> predicate)
{
return _objectSet.Single<T>(predicate);
}
/// <summary>
/// The first record matching the specified criteria
/// </summary>
/// <param name="predicate">Criteria to match on</param>
/// <returns>A single record containing the first record matching the specified criteria</returns>
public T First(Func<T, bool> predicate)
{
return _objectSet.First<T>(predicate);
}
/// <summary>
/// Deletes the specified entitiy
/// </summary>
/// <param name="entity">Entity to delete</param>
/// <exception cref="ArgumentNullException"> if <paramref name="entity"/> is null</exception>
public void Delete(T entity)
{
if (entity == null)
{
throw new ArgumentNullException("entity");
}
_objectSet.DeleteObject(entity);
}
/// <summary>
/// Deletes records matching the specified criteria
/// </summary>
/// <param name="predicate">Criteria to match on</param>
public void Delete(Func<T, bool> predicate)
{
IEnumerable<T> records = from x in _objectSet.Where<T>(predicate) select x;
foreach (T record in records)
{
_objectSet.DeleteObject(record);
}
}
/// <summary>
/// Dispose
/// </summary>
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
/// <summary>
/// Dispose
/// </summary>
/// <param name="disposing">A boolean value indicating whether or not to dispose managed resources</param>
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
if (_context != null)
{
_context.Dispose();
_context = null;
}
}
}
}
不知何故，我的反射技巧似乎是在 LINQ 语句中执行的，当我为 objectGroups 分配值时，这显然会引发异常。
LINQ to Entities 无法识别方法 'System.Object GetValue(System.Object, System.Object[])' 方法，并且此方法无法转换为存储表达式。
有任何想法吗 ？我真的需要保留存储库的通用性。我使用反射的所有方法都抛出异常......
非常感谢。
编辑：添加了大部分存储库的方法和接口。课程中可能缺少一些方法，但这样做是为了减轻阅读：)