I get this error in LINQ to Entities: LINQ to Entities does not recognize the method 'System.String ToString()' method.
How should I solve this common problem?
Note that FleetViewModel.DWTStart is a string and fleet.DWTStart is a nullable decimal.
var qry = from fleet in _entitiesContext.Fleets
select new FleetViewModel
{
FleetID = fleet.FleetID,
FleetName = fleet.FleetName,
DWTStart = fleet.DWTStart.HasValue?fleet.DWTStart.Value.ToString():"",
DWTEnd = fleet.DWTEnd.HasValue ? fleet.DWTEnd.Value.ToString() : ""
};
Thanks.
Basically you need to do the final part in-process, which you can force with AsEnumerable:
var qry = _entitiesContext.Fleets
.Select(fleet => new { fleet.FleetID,
fleet.FleetName,
fleet.DWTStart,
fleet.DWTEnd })
.AsEnumerable() // Do the rest in-process
.Select(fleet => new FleetViewModel {
FleetID = fleet.FleetID,
FleetName = fleet.FleetName,
DWTStart = fleet.DWTStart.HasValue?fleet.DWTStart.Value.ToString():"",
DWTEnd = fleet.DWTEnd.HasValue ? fleet.DWTEnd.Value.ToString() : ""
});
If there's nothing else in the entity apart from these four properties, you can skip the anonymous type to start with - it's really only there to avoid fetching data you don't need:
var qry = _entitiesContext.Fleets
.AsEnumerable() // Do the rest in-process
.Select(fleet => new FleetViewModel {
FleetID = fleet.FleetID,
FleetName = fleet.FleetName,
DWTStart = fleet.DWTStart.HasValue?fleet.DWTStart.Value.ToString():"",
DWTEnd = fleet.DWTEnd.HasValue ? fleet.DWTEnd.Value.ToString() : ""
});
Related
I have this query:
Project = await Context.Projects.Where(x => x.Id == project.Id)
.Select(x => new ProjectModel
{
Id = project.Id,
Name = project.Name,
TreeDataDict = x.Tasks.Select(y => new TreeItemModel()
{
NodeId = y.Id,
ParentId = SetTaskParentId(y, y.Type),
NodeTitle = y.Name,
Expanded = false,
Object = new TaskBaseModel
{
Milestone = y.Milestone,
StartDate = y.StartDate,
CurrentEndDate = y.CurrentEndDate,
EndDate = y.EndDate,
},
Icon = TaskHelper.GetTaskIcon(y.Type),
Children = new List<TreeItemModel>()
}).ToDictionary(y => y.NodeId, y => y)
}).SingleOrDefaultAsync();
and also tried like this:
Project = await Context.Projects.Where(x => x.Id == project.Id)
.Select(x => new ProjectModel
{
Id = project.Id,
Name = project.Name,
TreeDataDict = x.Tasks.ToDictionary(y => y.Id, y => new TreeItemModel(
{
NodeId = y.Id,
ParentId = SetTaskParentId(y, y.Type),
NodeTitle = y.Name,
Expanded = false,
Object = new TaskBaseModel
{
Milestone = y.Milestone,
StartDate = y.StartDate,
CurrentEndDate = y.CurrentEndDate,
EndDate = y.EndDate,
},
Icon = TaskHelper.GetTaskIcon(y.Type),
Children = new List<TreeItemModel>()
})
}).SingleOrDefaultAsync();
Both ways I got this exception:
What could be causing this? and is there a way I could make this work without fetching as a list and then covert it to dictionary? What could be the most efficient way to achieve this?
Regards
What could be causing this?
Translation of the nested ToDictionary call (none of the available overloads) is not supported. Consider it one of the (many) current (latest at the time of writing official v5.0.11) EF Core shortcomings.
Interestingly though, the Dictionary<TKey, TValue> constructor overload with IEnumerable<KeyValuePair<TKey, TValue>> argument as well as projection (Select) to KeyValuePair<TKey, TValue> is supported, which gives the workaround - replace the ToDictionary call with the aforementioned constructor and Select, e.g. (replace int with the type of the Id)
TreeDataDict = new Dictionary<int, TreeItemModel>(
x.Tasks.Select(y => new TreeItemModel()
{
NodeId = y.Id,
ParentId = SetTaskParentId(y, y.Type),
NodeTitle = y.Name,
Expanded = false,
Object = new TaskBaseModel
{
Milestone = y.Milestone,
StartDate = y.StartDate,
CurrentEndDate = y.CurrentEndDate,
EndDate = y.EndDate,
},
Icon = TaskHelper.GetTaskIcon(y.Type),
Children = new List<TreeItemModel>()
})
.Select(e => new KeyValuePair<int, TreeItemModel>(e.NodeId, e)));
This will fix the current error. But note that you are using other non-translatable constructs (custom method calls like SetTaskParentId(y, y.Type) and TaskHelper.GetTaskIcon(y.Type)) which are supported only in the final Select, so make sure to not add LINQ operator like Where, OrderBy etc. after the root query Select(x => new ProjectModel { ... }, otherwise you'll get other runtime errors. ToList, `First
I want to add a dummy member to an IQueryable and came up with this solution:
IQueryable<Geography> geographies = _unitOfWork.GeographyRepository.GetAll(); //DbSet<Geography>
var dummyGeographies = new Geography[] { new Geography { Id = -1, Name = "All" } }.AsQueryable();
var combinedGeographies = geographies.Union(dummyGeographies);
var test = combinedGeographies.ToList(); //throws runtime exc
But it throws the following exception:
Processing of the LINQ expression 'DbSet
.Union(EnumerableQuery { Geography, })' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core.
How could I make it work?!
you can only union on data structure which are the same
IQueryable is only applicable if the query expression not been been expressed (ToList) before its run against db and you want the expression modifiable . aka nothing which which is not going to db as a query needs to be IQueryable (simple explanation better to research and understand this yourself)
List<Geography> geographies = _unitOfWork.GeographyRepository
.GetAll() //DbSet<Geography>
.Select(o => new Geography { Id = o.Id, Name = o.Name })
.ToList();
List<Geography> dummyGeographies = new List<Geography>() {
new Geography[] { new Geography { Id = -1, Name = "All" } }
};
var combinedGeographies = geographies.Union(dummyGeographies);
var test = combinedGeographies.ToList();
I was able to achieve it with the following code:
IQueryable<Geography> geographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = o.Id, Name = o.Name });
IQueryable<Geography> dummyGeographies = _unitOfWork.GeographyRepository.GetAll().Select(o => new Geography { Id = -1, Name = "All" });
var combinedGeographies = geographies.Union(dummyGeographies);
How would I go about changing my if statement and foreach to something cleaner in linq using select and where.
I've tried to make the if statement into a where clause and then use the select query as a replacement for the Foreach loop but that seem to have type issues and wasn't working.
{
StripeConfiguration.ApiKey = _appSettings.StripeSecretKey;
var profile = await _userManager.FindByIdAsync(customerServiceID);
var stripeId = profile.StripeAccountId;
if (stripeId == null)
throw new ArgumentException("No associated Stripe account found.");
List<PaymentMethodDto> result = new List<PaymentMethodDto>();
var options = new PaymentMethodListOptions
{
Customer = stripeId,
Type = "card",
};
var service = new PaymentMethodService();
var payments = await service.ListAsync(options);
if (payments != null && payments.Data?.Count > 0)
{
payments.Data.ForEach((x) =>
{
result.Add(
new PaymentMethodDto
{
Brand = x.Card.Brand,
LastDigits = x.Card.Last4,
StripeToken = x.Id,
CustomerID = x.CustomerId
});
});
}
return result;
}
Just do a regular Select.
List<PaymentMethodDto> result = payments.Data.Select(x => new PaymentMethodDto
{
Brand = x.Card.Brand,
LastDigits = x.Card.Last4,
StripeToken = x.Id,
CustomerID = x.CustomerId
})
.ToList();
If payments.Data has nothing in it, this will give you an empty list, which is what you want.
If payments is null, you'll get an exception, which I think if you think about it really hard is probably what you really want in that case too. Why would .ListAsync() yield a null value?
i have been finding problems related to the following code..Actually i want to select filtered records but it gives me 0 records. I have tried the following. Please Help me..
public static IEnumerable<PostModel> GetPostData(string cat)
{
var data = new LinqClassDataContext(); IEnumerable<PostModel> pm;
pm=data.PostTables.Where(Post => new PostModel
{ CategoryName= Post.CategoryName}.Equals(cat)).Select
(Post => new PostModel
{ PostID = (int)Post.PostID,
PostSubject = Post.PostSubject,
PostAuthor = Post.PostAuthor,
PostDate = Post.PostDate,
PostContent = Post.PostContent,
CategoryName = Post.CategoryName
});
}
Why your PostModel class object would be Equals string cat?
Maybe you meant:
data.PostTables.Where(Post => Post.CategoryName == cat)
Even though you overrided Equals method on PostModel I think you should use line I meantioned above because it is more obvious.
Also at the end of query you should call .ToList() method for initiating it. And you should dispose context after creating it in the method.
public static IEnumerable<PostModel> GetPostData(string cat)
{
var data = new LinqClassDataContext();
var pm = data.PostTables.Where(post => post.CategoryName == cat)
.Select(Post => new PostModel
{
PostID = (int)Post.PostID,
PostSubject = Post.PostSubject,
PostAuthor = Post.PostAuthor,
PostDate = Post.PostDate,
PostContent = Post.PostContent,
CategoryName = Post.CategoryName
})
.ToList();
data.Dispose();
return pm;
}
I'm trying to implement a T-SQL equivalent of a where in (select ...) code in LINQ.
This is what I have now:
int contactID = GetContactID();
IEnumerable<string> threadList = (from s in pdc.Messages
where s.ContactID == contactID
group 1 by new { s.ThreadID } into d
select new { ThreadID = d.Key.ThreadID}).ToList<string>();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group new { s } by new { s.ThreadID } into d
let maxMsgID = d.Where(x => x.s.ContactID != contactID).Max(x => x.s.MessageID)
select new {
LastMessage = d.Where(x => x.s.MessageID == maxMsgID).SingleOrDefault().s
};
However, my code won't compile due to this error for the ToList():
cannot convert from
'System.Linq.IQueryable<AnonymousType#1>'
to
'System.Collections.Generic.IEnumerable<string>'
Anyone have any suggestions on how to implement this? Or any suggestions on how to simplify this code?
Your query returns a set of anonymous types; you cannot implicitly convert it to a List<string>.
Instead, you should select the string itself. You don't need any anonymous types.
Change it to
var threadList = pdc.Messages.Where(s => s.ContactID == contactID)
.Select(s => s.ThreadID)
.Distinct()
.ToList();
var result = from s in pdc.Messages
where threadList.Contains(s.ThreadID)
group s by s.ThreadID into d
let maxMsgID = d.Where(x => x.ContactID != contactID).Max(x => x.MessageID)
select new {
LastMessage = d.Where(x => x.MessageID == maxMsgID).SingleOrDefault()
};