I'm trying to create a Repository for an Object Page
.
I would like to have non-generic LINQ queries but can't seem to get them working,
I am only able to create them if they are generic and in a helper class, and please let me know if it is recommended to have this type of function in a Helper Class, let me know the reasoning if so.
public class PageRepository
{
public PageViewModel GetPageById(string oid)
{
using (var db = new AppDbContext())
{
Page page = db.Pages
//This is what I cannot get working
.WhereStatusType(StatusType.Published);
return GetPageView(page);
}
}
//I would like the below to work
//Tried generic (below), also non-generic <Page> but doesn't work
internal static IQueryable<T> WhereStatusType<T>(this IQueryable<T> query, StatusType statusType = StatusType.Published)
where T : Page
{
return query.Where(p => p.StatusType == statusType);
}
}
//Below is working, but don't want it in a helper
public static class PageHelper
{
internal static IQueryable<T> WhereStatusType<T>(this IQueryable<T> query, StatusType statusType = StatusType.Published)
where T : Page
{
return query.Where(p => p.StatusType == statusType);
}
}
When I attempt to make the IQueryable non-generic, I receive the following errors:
public class PageRepository has an issue:
Extension method must be defined in a non-generic static class
Also:
'IQueryable' does not contain a definition for 'WhereStatusType' and no extension method 'WhereStatusType' accepting a first argument of type 'IQueryable' could be found (are you missing a using directive or an assembly reference?)
I'm sure it is a simple solution, thank you for the help. Also, if I am approaching this incorrectly, any advice would be greatly appreciated.
While FirstOfDefault() is suggested for the above code, I am also looking to use the function when returning List<PageViewModel>
(I may have over-simplified the code/example), for example:
public List<PageViewModel> GetPages()
{
using (var context = new AppDbContext())
{
List<Page> pages = new List<Page>();
pages = context.Pages.AsNoTracking()
.WhereStatusType(StatusType.Published)
.ToList();
if (pages != null)
{
List<PageViewModel> pageViewModels = new List<PageViewModel>();
foreach (Page p in pages)
pageViewModels.Add(GetPageView(p));
return pageViewModels;
}
else
return null;
}
}
The error message tells you exactly what's going on here. If you want an extension method -- a method whose first parameter uses the this
keyword, like your example -- then it needs to be defined in a non-generic static class, like your PageHelper
.
If you don't like that approach, you could define a non-extension method, something like this:
public class PageRepository
{
public PageViewModel GetPageById(string oid)
{
using (var db = new AppDbContext())
{
Page page = GetPagesWithStatus(db.Pages, StatusType.Published);
return GetPageView(page);
}
}
internal IQueryable<Page> GetPagesWithStatus(IQueryable<Page> query, StatusType statusType)
{
return query.Where(p => p.StatusType == statusType);
}
}
As @asherber mentioned, your LINQ query isn't right. You are comparing p.Alias
to p.Alias
Also, it looks like you want a FirstOrDefault()
in there.
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