This is a .NET Core Web API Task method. I have a flat table that I need to convert into a nested DTOs. The first DTO works but I can't seem to get the second DTO to nest after grouping.
I know I have done the grouping correctly. I am just not sure the second level nesting of the DTO is done correctly, it complains about not being able to translate to some type.
LINQ Query to put data in a nested object
Can someone point me in the right track?
public async Task<List<PointCardViewModel>> GetPointCards() {
var data = (from s in db.Students
join dc in db.DailyCards on s.StudentId equals dc.StudentId
join dcli in db.DailyCardLineItems on dc.CardId equals dcli.CardId
join dcob in db.DailyCardOtherBehaviors on dc.CardId equals dcob.CardId
select new
{
s.StudentName,
s.StudentGrade,
dc.CardId,
dc.CardDate,
dcli.ClassParticipationPoints,
dcli.AssignmentCompletionPoints,
dcli.BonusHomeworkPoints,
dcli.ClassPeriod,
dcob.PersonalAppearancePoints,
dcob.LunchPoints,
dcob.RecessOtherPoints,
dcob.AmHomeroomPoints,
dcob.PmHomeroomPoints
});
var queryPointCards = (data
.GroupBy(x => new
{
x.CardId,
x.StudentGrade,
x.StudentName,
x.CardDate,
x.PersonalAppearancePoints,
x.LunchPoints,
x.RecessOtherPoints,
x.AmHomeroomPoints,
x.PmHomeroomPoints
})
.Select(x => new PointCardViewModel()
{
CardId = x.Key.CardId,
StudentName = x.Key.StudentName,
Grade = x.Key.StudentGrade,
EvaluationDate = x.Key.CardDate,
PersonalAppearancePoints = x.Key.PersonalAppearancePoints,
LunchPoints = x.Key.LunchPoints,
RecessOtherPoints = x.Key.RecessOtherPoints,
AMHomeRoomPoints = x.Key.AmHomeroomPoints,
PMHomeRoomPoints = x.Key.PmHomeroomPoints,
//LineItems = null --> This works!! But not the below
LineItems = x.Select(c => new LineItemViewModel
{
ClassPeriod = c.ClassPeriod,
BonusHomeworkPoints = c.BonusHomeworkPoints,
ClassParticipationPoints = c.ClassParticipationPoints,
AssignmentCompletionPoints = c.AssignmentCompletionPoints
})
}
)
).ToListAsync();
if (db != null)
{
return await queryPointCards;
}
return null;
}
You have hit limitation of Grouping. After groping you cannot access to group items. Only fields from 'Key' and aggregation functions are allowed.
So just put data.AsEnumerable() and do grouping on the client side.
Related
I have a query that looks like this:
var caseList = (from x in context.Cases
where allowedCaseIds.Contains(x => x.CaseId)
select new Case {
CaseId = x.CaseId,
NotifierId = x.NotifierId,
Notifier = x.NotifierId.HasValue ? new Notifier { Name = x.Notifier.Name } : null // This line throws exception
}).ToList();
A Case class can have 0..1 Notifier
The query above will result in the following System.NotSupportedException:
Unable to create a null constant value of type 'Models.Notifier'. Only entity types, enumeration types or primitive types are supported
in this context.
At the moment the only workaround I found is to loop the query result afterwards and manually populate Notifierlike this:
foreach (var c in caseList.Where(x => x.NotifierId.HasValue)
{
c.Notifier = (from x in context.Notifiers
where x.CaseId == c.CaseId
select new Notifier {
Name = x.Name
}).FirstOrDefault();
}
But I really don't want to do this because in my actual scenario it would generate hundreds of additional queries.
Is there any possible solution for a situation like this?.
I think you need to do that in two steps. First you can fetch only the data what you need with an anonymous type in a single query:
var caseList = (from x in context.Cases
where allowedCaseIds.Contains(x => x.CaseId)
select new {
CaseId = x.CaseId,
NotifierId = x.NotifierId,
NotifierName = x.Notifier.Name
}).ToList();
After that, you can work in memory:
List<Case> cases = new List<Case>();
foreach (var c in caseList)
{
var case = new Case();
case.CaseId = c.CaseId;
case.NotifierId = c.NotifierId;
case.NotifierName = c.NotifierId.HasValue ? c.NotifierName : null;
cases.Add(case);
}
You could try writing your query as a chain of function calls rather than a query expression, then put an .AsEnumerable() in between:
var caseList = context.Clases
.Where(x => allowedCaseIds.Contains(x.CaseId))
.AsEnumerable() // Switch context
.Select(x => new Case() {
CaseId = x.CaseId,
NotifierId = x.NotifierId,
Notifier = x.NotifierId.HasValue
? new Notifier() { Name = x.Notifier.Name }
: null
})
.ToList();
This will cause EF to generate an SQL query only up to the point where you put the .AsEnumerable(), further down the road, LINQ to Objects will do all the work. This has the advantage that you can use code that cannot be translated to SQL and should not require a lot of changes to your existing code base (unless you're using a lot of let expressions...)
Here's my code:
var myStrings = (from x in db1.MyStrings.Where(x => homeStrings.Contains(x.Content))
join y in db2.MyStaticStringTranslations on x.Id equals y.id
select new MyStringModel()
{
Id = x.Id,
Original = x.Content,
Translation = y.translation
}).ToList();
And I get the error that the specified LINQ expression contains references to queries that are associated with different contexts. I know that the problem is that I try to access tables from both db1 and db2, but how do I fix this?
MyStrings is a small table
Load filtered MyStrings in memory, then join with MyStaticStringTranslations using LINQ:
// Read the small table into memory, and make a dictionary from it.
// The last step will use this dictionary for joining.
var byId = db1.MyStrings
.Where(x => homeStrings.Contains(x.Content))
.ToDictionary(s => s.Id);
// Extract the keys. We will need them to filter the big table
var ids = byId.Keys.ToList();
// Bring in only the relevant records
var myStrings = db2.MyStaticStringTranslations
.Where(y => ids.Contains(y.id))
.AsEnumerable() // Make sure the joining is done in memory
.Select(y => new {
Id = y.id
// Use y.id to look up the content from the dictionary
, Original = byId[y.id].Content
, Translation = y.translation
});
You are right that db1 and db2 can't be used in the same Linq expression. x and y have to be joined in this process and not by a Linq provider. Try this:
var x = db1.MyStrings.Where(xx => homeStrings.Contains(xx.Content)).ToEnumerable();
var y = db2.MyStaticStringTranslations.ToEnumerable();
var myStrings = (from a in x
join b in y on x.Id equals y.id
select new MyStringModel()
{
Id = x.Id,
Original = x.Content,
Translation = y.translation
}).ToList();
Refer to this answer for more details: The specified LINQ expression contains references to queries that are associated with different contexts
dasblinkenlight's answer has a better overall approach than this. In this answer I'm trying to minimize the diff against your original code.
I also faced the same problem:
"The specified LINQ expression contains references to queries that are associated with different contexts."
This is because it's not able to connect to two context at a time so i find the solution as below.
Here in this example I want to list the lottery cards with the owner name but the Table having the owner name is in another Database.So I made two context DB1Context and DB2Context.and write the code as follows:
var query = from lc in db1.LotteryCardMaster
from om in db2.OwnerMaster
where lc.IsActive == 1
select new
{
lc.CashCardID,
lc.CashCardNO,
om.PersonnelName,
lc.Status
};
AB.LottryList = new List<LotteryCardMaster>();
foreach (var result in query)
{
AB.LottryList.Add(new LotteryCardMaster()
{
CashCardID = result.CashCardID,
CashCardNO = result.CashCardNO,
PersonnelName =result.PersonnelName,
Status = result.Status
});
}
but this gives me the above error so i found the other way to perform joining on two tables from diffrent database.and that way is as below.
var query = from lc in db1.LotteryCardMaster
where lc.IsActive == 1
select new
{
lc.CashCardID,
lc.CashCardNO,
om.PersonnelName,
lc.Status
};
AB.LottryList = new List<LotteryCardMaster>();
foreach (var result in query)
{
AB.LottryList.Add(new LotteryCardMaster()
{
CashCardID = result.CashCardID,
CashCardNO = result.CashCardNO,
PersonnelName =db2.OwnerMaster.FirstOrDefault(x=>x.OwnerID== result.OwnerID).OwnerName,
Status = result.Status
});
}
In the DB, I have a two tables with a one-to-many relationship:
orders suborders
----------- -----------
id id
name order_id
name
I'd like to query these tables and end up with a list of order objects, each of which contains a list (or empty list) of suborder objects. I'd also like to do this in a single DB query so it performs well.
In traditional SQL query land, I'd do something like (forgive the pseudocode):
rs = "select o.id, o.name, so.id, so.name from orders o left join suborders so on o.id = so.order_id order by o.id"
orders = new List<Order>
order = null
foreach (row in rs) {
if (order == null || row.get(o.id) != order.id) {
order = new Order(row.get(o.id), row.get(o.name), new List<Suborders>)
orders.add(order)
}
if (row.get(so.id) != null) {
order.suborders.add(new Suborder(row.get(so.id) row.get(so.name))
}
}
Is there a way to get this same resulting object structure using LINQ-to-Entities? Note that I want to get new objects out of the query, not the Entity Framework generated objects.
The following gets me close, but throws an exception: "LINQ to Entities does not recognize the method..."
var orders =
(from o in Context.orders
join so in Context.suborders on o.id equals so.order_id into gj
select new Order
{
id = o.id,
name = o.name,
suborders = (from so in gj select new Suborder
{
so.id,
so.name
}).ToList()
}).ToList();
The solution ends up being pretty simple. The key is to use a group join to get SQL to do the left join to suborders, and add a second ToList() call to force the query to be run so you're not trying to do object creation on the SQL server.
orders = Context.orders
.GroupJoin(
Context.suborders,
o => o.id,
so => so.order_id,
(o, so) => new { order = o, suborders = so })
.ToList()
.Select(r => new Order
{
id = r.order.id,
name = r.order.name,
suborders = r.suborders.Select(so => new Suborder
{
id = so.id,
name = so.name
}.ToList()
}).ToList();
This code only makes a single query to SQL for all objects and their child objects. It also lets you transform the EF objects into whatever you need.
I Always create a virtualized Property for Relations
so just extend (add a property) to your order class :
public class Order{
...
List<Suborder> _suborders;
public List<Suborder> Suborders{
get {
return _suborders ?? (_suborders = MyContext.Suborders.Where(X=>X.order_id==this.id).ToList());
}
...
}
so data will be fetched (pulled) only when you call the getters
How about this code ?
You can get a local cache.
List<Orders> orders = new List<Orders>();
private void UpdateCache(List<int> idList)
{
using (var db = new Test(Settings.Default.testConnectionString))
{
DataLoadOptions opt = new DataLoadOptions();
opt.LoadWith<Orders>(x => x.Suborders);
db.LoadOptions = opt;
orders = db.Orders.Where(x => idList.Contains(x.Id)).ToList();
}
}
private void DumpOrders()
{
foreach (var order in orders)
{
Console.WriteLine("*** order");
Console.WriteLine("id:{0},name:{1}", order.Id, order.Name);
if (order.Suborders.Any())
{
Console.WriteLine("****** sub order");
foreach (var suborder in order.Suborders)
{
Console.WriteLine("\torder id:{0},id{1},name:{2}", suborder.Order_id, suborder.Id, suborder.Name);
}
}
}
}
private void button1_Click(object sender, EventArgs e)
{
UpdateCache(new List<int> { 0, 1, 2 });
DumpOrders();
}
Output example below
*** order
id:0,name:A
****** sub order
order id:0,id0,name:Item001
order id:0,id1,name:Item002
order id:0,id2,name:Item003
*** order
id:1,name:B
****** sub order
order id:1,id0,name:Item003
*** order
id:2,name:C
****** sub order
order id:2,id0,name:Item004
order id:2,id1,name:Item005
I have a rather complex linq to entity query that I'm performing, in the end, I have a result set. I loop through that result set, build business objects and return that list of business objects. it's pretty quick, the problem is that 2 of the child properties are complex objects with their own child objects. for every business object in my loop, I then have to make 2 DB calls to fill its child object. Those 2 calls slow down the overall process, is there a better way to do this? noob to EF here. (EF 4,SQL Server 2008,c#)
Get a result set:
var newresult = from r in result // result is another complex query
join subedit in
(from sa in context.Security_Access
join g in context.Security_UserGroup on sa.EntityID equals g.GroupID
where (sa.PrivledgeID == xx) && g.UserID == userId
select new { user = g.UserID, linkid = sa.LinkID }).Distinct() on new { aid = r.AssetId } equals new { aid = subedit.linkid } into theSubEdit
from subEditAccess in theSubEdit.DefaultIfEmpty()
join subdownload in
(from sa in context.Security_Access
join g in context.Security_UserGroup on sa.EntityID equals g.GroupID
where (sa.PrivledgeID == xx|| sa.PrivledgeID == yy) && g.UserID == userId
select new { user = g.UserID, linkid = sa.LinkID }).Distinct() on new { aid = r.AssetId } equals new { aid = subdownload.linkid } into theSubDownload
from subDownloadAccess in theSubDownload.DefaultIfEmpty()
join subView in
(from sa in context.Security_Access
join g in context.Security_UserGroup on sa.EntityID equals g.GroupID
where (sa.PrivledgeID == xx|| sa.PrivledgeID == yy|| sa.PrivledgeID == 101) && g.UserID == userId
select new { user = g.UserID, linkid = sa.LinkID }).Distinct() on new { aid = r.AssetId } equals new { aid = subView.linkid } into theSubView
from subViewAccess in theSubView.DefaultIfEmpty()
select new { r, EditAccess = (int?)subEditAccess.user, DownloadAccess = (int?)subDownloadAccess.user, ViewAccess = (int?)subViewAccess.user };
I then loop through that result set:
foreach (var asset in newresult)
{
// and build a new business object, set its properties
BoAsset boAsset = new BoAsset();
boAsset.HasEditRights = (asset.EditAccess > 0);
boAsset.HasDownloadRights = (asset.DownloadAccess > 0);
boAsset.HasViewRights = (asset.ViewAccess > 0);
boAsset.Description = asset.r.Description;
boAsset.DetailedDescription = asset.r.DetailedDescription;
boAsset.Keywords = asset.r.Keywords;
boAsset.Notes = asset.r.Notes;
boAsset.Photographer = asset.r.Photographer;
boAsset.PhotographerEmail = asset.r.PhotographerEmail;
boAsset.Notes = asset.r.Notes;
boAsset.Author = asset.r.Author;
// these 2 properties i've commented out are
// complex objects/entities, setting them the way I am
// requires me to call 2 separate methods which make 2 DB trips
// per business object.
//boAsset.Domains = GetAssetDomains(asset.r.AssetId);
//boAsset.DomainEntries = GetAssetCustomDomains(asset.r.AssetId);
myListofObjects.Add(boAsset);
}
return myListofObjects;
Is there a better way?
Just add this .Include("Domains").Include("DomainEntries") to your Linq in in context.Security_Access That should get rows from those tables all in one go.
So your "inner" queries would look like:
from sa in context.Security_Access.Include("Domains").Include("DomainEntries")
join g in context.Security_UserGroup on sa.EntityID equals g.GroupID
where (sa.PrivledgeID == xx) && g.UserID == userId
select new { ...
Here is the documentation from MS: http://msdn.microsoft.com/en-us/library/bb738708.aspx
If you want to improve your performance use compile queries !
You can check the example here.
static readonly Func<AdventureWorksEntities, Decimal,
IQueryable<SalesOrderHeader>> s_compiledQuery2 =
CompiledQuery.Compile<AdventureWorksEntities, Decimal, IQueryable<SalesOrderHeader>>((ctx, total) =>
from order in ctx.SalesOrderHeaders.Include("Orders") where order.TotalDue >= total select order);
MSDN
AND
You can Introduce Include suppose to select all the employees along with their departments . If you have a navigational property, you won't need a join at all. You can use Include like this:
List<Employee> employeesWithDepartments = CreateObjectSet<Employee>().
Include(e => e.Department).
ToList();
I have two tables in my database, Building and Town. They look like this:
Building:
buildingid
buildingname
Town:
id
userid
buildingid
In Town there is one entry for each building a user has.
What i want is to populate a GridView for a user with a given userid. This GridView should include the buildingname and the number of buildings.
Building. I have tried this:
var buildings = (from Town in dc.Towns
join Building in dc.Buildings
on Town.buildingid equals Building.buildingid
select Building.buildingname);
gvBuildings.DataSource = buildings;
gvBuildings.DataBind();
But I don't know how to get the numbers for each building.
I have now been working on this for a while and a couple of your answers work. I have used this code:
var buildings = dc.Towns
.Where(t => t.userid == userid)
.GroupJoin(dc.Buildings,
t => t.buildingid,
b => b.buildingid,
(Town, Buildings) => new
{
BuildningName = Buildings.First().buildingname,
Count = Buildings.Count()
});
gvBuildings.DataSource = buildings.ToList();
gvBuildings.DataBind();
When i run this code my GridView ends up looking like this:
I need the buildings to be shown in groups, grouped by the buildingname. I have tried all of the suggestions but i cant get it to work.
Try grouping:
var buildings = dc.Towns
.Where(t => t.UserId == userId)
.GroupJoin(dc.Buildings,
t => t.BuildingId,
b => b.BuildingId,
(town, buildings) => new
{
BuildingName = buildings.First().BuildingName,
Count = buildings.Count
});
Keep in mind that when binding to a control you must supply a collection of type (or implementing) IList. This can be accomplished by calling ToList() on the buildings collection:
gvBuildings.DataSource = buildings.ToList();
gvBuildings.DataBind();
check linq differed execution
and than try the blow code might work for you
var buildings =
(from j in dc.Town
join i in dc.Buildings
on j.buildingId equals i.buildingId
where j.Userid = varUSerid
group new {i, j}
by new
{ i.BuildingID }
into
g
select new {
BuildingName = g.First<k=>k.BuildingName)
, count = g.Count() } ).ToList();
gvBuildings.DataSource = buildings;
gvBuildings.DataBind();
var buildings = (from Town in dc.Towns
join Building in dc.Buildings
on Town.buildingid equals Building.buildingid
into results
from r in results.DefaultIfEmpty()
group Town by new
{
r.BuildingId
} into groupedResults
where Town.UserID == parameteruserId
select new
{
BuildingName = Building.buildingname,
BuildingCount = groupedResults.Count()
});
Try this.. it should work.. i have a similar requirement..
manDbDataContext db = new DbDataContext();
var estimatedTotal = ( from est in db.AssignmentEstimatedMaterials
where est.assignment_id == Convert.ToInt32(Label_assignmentId.Text)
join materialdetail in db.Materials on est.material_id equals materialdetail.material_id
select new { est.qty,est.total_amount, materialdetail.material_name}).ToList();
GridView_estiamte_material.DataSource = estimatedTotal;
GridView_estiamte_material.DataBind();
Note, you should select individual data and it works.