如何使用委托通过名称获取 CompiledQuery

Question

我正在尝试查找并运行给定名称的 CompiledQuery。如何按名称访问已编译的查询，然后如何调用委托？

这是我所能得到的 - 我收到错误“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);

//其他编译查询省略，但结果是实现了通用接口IProjectObject的IQueryable对象

    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
         }
     }
}

Answer 1

您可能会采取一些冗长的方法来尝试使用 DataContext 作为返回 IQueryable 的第一个参数来识别 Func<...> 类型的任何字段，但是您可能会发现仅添加自定义属性要容易得多：

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

...然后您可以将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);

然后您可以根据它选择查询及其名称：

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:)