[英]how to use a delegate to get by name a CompiledQuery
我正在嘗試查找並運行給定名稱的CompiledQuery。 如何按名稱訪問已編譯的查詢,然后如何調用委托?
這是我所能得到的-我收到錯誤“錯誤綁定到目標方法”
public class ActivityRepository
{
private readonly ActivityDataContext _db;
public ActivityRepository()
{
_db = new ActivityDataContext();
}
public static Func<ActivityDataContext, int, IQueryable<ProjectObject>>
GetCompiledLatestProjects = CompiledQuery.Compile
((ActivityDataContext db, int projectId) =>
from c in db.projectObjects
where c.projectId == projectId
select c);
public static Func<ActivityDataContext, Guid, IQueryable<Report>>
GetCompiledReports = CompiledQuery.Compile
((ActivityDataContext db, Guid itemId) =>
from c in db.Reports
where c.reportObjectId == itemId
select c);
//省略其他已編譯的查詢,但是結果是實現公共接口IProjectObject的IQueryable對象
delegate IQueryable<IProjectObject> MyDelegate();
static MyDelegate GetByName(object target, string methodName)
{
return (MyDelegate)Delegate.CreateDelegate
(typeof(MyDelegate), target, methodName);
}
public IList<Results> GetResults(string reportName)
{
IQueryable<ProjectObject> projectItems = GetLatestProjectObjects(projectId, quantity);
foreach (projectObject o in projectItems)
{
MyDelegate del = GetByName(this, reportName);
var dbReport = (IProjectObject) GetCompiledReports(_db, o.itemId).FirstOrDefault();
// add results to List and return
}
}
}
您可能可以采取一些漫長的嘗試來嘗試識別類型為Func <...>的任何字段,並將DataContext作為返回IQueryable的第一個參數,但是您可能發現添加一個自定義屬性要容易得多:
[AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
public class DynamicQueryAttribute : Attribute { }
...然后您可以將其添加到您的字段中:
[DynamicQuery]
public static Func<ActivityDataContext, int, IQueryable<ProjectObject>>
GetCompiledLatestProjects = CompiledQuery.Compile
((ActivityDataContext db, int projectId) =>
from c in db.projectObjects
where c.projectId == projectId
select c);
然后,您可以基於該查詢及其名稱選擇查詢:
public static IQueryable<IProjectObject> ExecuteQuery(Type ownerType, string name, params object[] args)
{
var query = typeof(ownerType)
.GetFields(BindingFlags.Public | BindingFlags.Static)
.Where(f =>
(f.GetCustomAttributes(typeof(DynamicQueryAttribute), false).Length > 0)
&& (f.Name.ToLowerInvariant() == name.ToLowerInvariant()))
.Select(f => (Delegate) f.GetValue(null))
.SingleOrDefault();
if (query == null)
return null;
return (IQueryable<IReportObject>)query.DynamicInvoke(args);
}
用法:
var results = ExecuteQuery(
typeof(ActivityRepository),
"GetCompiledLatestProjects",
dataContext,
projectId);
希望有幫助:)
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