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如何使用委托按名称获取CompiledQuery

linq.compiledquery typeof delegates linq c#

0

Andrew · 技术社区 · 14 年前

我正在尝试查找并运行名为的已编译查询。如何按名称访问已编译的查询,然后如何调用委托?

这里是我能得到的-我得到错误'错误绑定到目标方法'

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);

    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
         }
     }
}

1 回复 | 直到 14 年前

1

0

Matthew Abbott 14 年前

[AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
public class DynamicQueryAttribute : Attribute { }

…然后可以添加到字段中:

[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,您可以基于此选择查询及其名称:

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);

希望有帮助:)