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
Related
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.
Sorry for strange title of the question, but I don't know how to formulate it more short. If you know how to formulate it better, I will be glad if you edit my question.
So, I have the following table:
I'm tolking about CustomerId and EventType fields. The rest is not important. I think you understand that this table is something like log by customers events. Some customer make event - I have event in the table. Simple.
I need to choice all customers events where each customer had event with type registration and type deposit. In other words, customer had registration before? The same customer had deposit? If yes and yes - I need to select all events of this customer.
How I can do that with the help of LINQ?
So I can write SQL like
select *
From "CustomerEvents"
where "CustomerId" in (
select distinct "CustomerId"
from "CustomerEvents"
where "EventType" = 'deposit'
intersect
select distinct "CustomerId"
from "CustomerEvents"
where "EventType" = 'registration'
)
It works, but how to write it on LINQ?
And second question. SQL above works, but not it is not universal. What if tomorrow I will need to show events of customers who have registration, deposit and - new one event - visit? I have to write new one query. Like:
select *
From "CustomerEvents"
where "CustomerId" in (
select "CustomerId"
from "CustomerEvents"
where "EventType" = 'deposit'
intersect
select distinct "CustomerId"
from "CustomerEvents"
where "EventType" = 'registration'
intersect
select distinct "CustomerId"
from "CustomerEvents"
where "EventType" = 'visit'
)
Uncomfortable :(
As source data, I have List with event types. Is there some way to make it dynamically? I mean, I have new one event in the list - I have new one intersect.
P.S I use Postgres and .NET Core 3.1
Update
I pine here a scheme
I haven't tested to see if this will translate to SQL correctly, but if we assume ctx.CustomerEvents is DbSet<CustomerEvent> you could try this:
var targetCustomerIds = ctx
.CustomerEvents
.GroupBy(event => event.CustomerId)
.Where(grouped =>
grouped.Any(event => event.EventType == "deposit")
&& grouped.Any(event => event.EventType == "registration"))
.Select(x => x.Key)
.ToList();
and then select all events for these customers:
var events = ctx.CustomerEvents.Where(event => targetCustomerIds.Contains(event.CustomerId));
To get targetCustomerIds dynamically with a variable number of event types, you could try this:
// for example
var requiredEventTypes = new [] { "deposit", "registration" };
// First group by customer ID
var groupedByCustomerId = ctx
.CustomerEvents
.GroupBy(event => event.CustomerId);
// Then filter out any grouping which doesn't satisfy your condition
var filtered = GetFilteredGroups(groupedByCustomerId, requiredEventTypes);
// Then select the target customer IDs
var targetCustomerIds = filtered.Select(x => x.Key).ToList();
// Finally, select your target events
var events = ctx.CustomerEvents.Where(event =>
targetCustomerIds.Contains(event.CustomerId));
You can define the GetFilteredGroups method like this:
private static IQueryable<IGrouping<int, CustomerEvent>> GetFilteredGroups(
IQueryable<IGrouping<int, CustomerEvent>> grouping,
IEnumerable<string> requiredEventTypes)
{
var result = grouping.Where(x => true);
foreach (var eventType in requiredEventTypes)
{
result = result.Where(x => x.Any(event => event.EventType == eventType));
}
return result;
}
Alternatively, instead of selecting the target customer IDs, you can try to directly select your target events from the filtered groupings:
// ...
// Filter out any grouping which doesn't satisfy your condition
var filtered = GetFilteredGroups(groupedByCustomerId, requiredEventTypes);
// Select your events here
var results = filtered.SelectMany(x => x).Distinct().ToList();
Regarding the inability to translate the query to SQL
Depending on your database size and particularly on the size of CustomerEvents table, this solution may or may not be ideal, but what you could do is load the optimized collection to memory and perform the grouping there:
// for example
var requiredEventTypes = new [] { "deposit", "registration" };
// First group by customer ID, but load into memory
var groupedByCustomerId = ctx
.CustomerEvents
.Where(event => requiredEventTypes.Contains(event.EventType))
.Select(event => new CustomerEventViewModel
{
Id = event.Id,
CustomerId = event.CustomerId,
EventType = event.EventType
})
.GroupBy(event => event.CustomerId)
.AsEnumerable();
// Then filter out any grouping which doesn't satisfy your condition
var filtered = GetFilteredGroups(groupedByCustomerId, requiredEventTypes);
// Then select the target customer IDs
var targetCustomerIds = filtered.Select(x => x.Key).ToList();
// Finally, select your target events
var events = ctx.CustomerEvents.Where(event =>
targetCustomerIds.Contains(event.CustomerId));
You will need to create a type called CustomerEventViewModel like this (so you don't have to load the entire CustomerEvent entity instances to memory):
public class CustomerEventViewModel
{
public int Id { get; set; }
public int CustomerId { get; set; }
public string EventType { get; set; }
}
And change the GetFilteredGroups like this:
private static IEnumerable<IGrouping<int, CustomerEvent>> GetFilteredGroups(
IEnumerable<IGrouping<int, CustomerEvent>> grouping,
IEnumerable<string> requiredEventTypes)
{
var result = grouping.Where(x => true);
foreach (var eventType in requiredEventTypes)
{
result = result.Where(x => x.Any(event => event.EventType == eventType));
}
return result;
}
It should now work fine.
Thank you for #Dejan Janjušević. He is excpirienced developer. But it seems EF can't translate him solution to SQL (or just my hands grow from wrong place). I publish here my solution for this situation. It's simple stuped. So. I have in the table EventType. It is string. And I have from the client the following filter request:
List<string> eventType
Just list with event types. So, in the action I have the following code of the filter:
if (eventType.Any())
{
List<int> ids = new List<int>();
foreach (var e in eventType)
{
var customerIdsList =
_context.customerEvents.Where(x => x.EventType == e).Select(x => x.CustomerId.Value).Distinct().ToList();
if (!ids.Any())
{
ids = customerIdsList;
}
else
{
ids = ids.Intersect(customerIdsList).ToList();
}
}
customerEvents = customerEvents.Where(x => ids.Contains(x.CustomerId.Value));
}
Not very fast, but works.
I'm looking for the counterpart of Msql query:
SELECT per.*,add.addressDescription FROM Persons per
JOIN Address add ON per.AddressId = add.AddressId
I have this query:
var query = persons.JOIN(address,per = person.addressId,add = addressId
(per,add) =>
new Persons{
addressDescription = add.addressDescription,
PersonId = per.PersonId,
PersonFirstName = per.PersonFirstName
PersonLastName = per.PersonLastName})
Is there a way to populate Persons.addressDescription without assigning individually the other properties of Persons? Imagine if Persons have 10 more properties.
I would like to refrain from using loops like:
foreach(Person person in PersonList)
{
foreach(Address address in AddressList)
{
if(person.addressId == address.addressId){
person.addressDescription = address.addressDescription
}
}
}
var query = persons.join(address,
per = person.addressId,
add = addressId
(per,add) =>
{
per.addressDescription = add.addressDescription;
return per;
});
var id = 1;
var query = database.Posts // your starting point - table in the "from" statement
.Join(database.Post_Metas, // the source table of the inner join
post => post.ID, // Select the primary key (the first part of the "on" clause in an sql "join" statement)
meta => meta.Post_ID, // Select the foreign key (the second part of the "on" clause)
(post, meta) => new { Post = post, Meta = meta }) // selection
.Where(postAndMeta => postAndMeta.Post.ID == id); // where statement
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.