I've written a LINQ query shown below :
List<Actions> actions = resourceActions.Actions.Select(s => s.ActionName).ToList();
How do I give for selecting multiple columns here ? ie I want to add columns s.ActionId and s.IsActive. I'm unable to apply it.
Make a class to represent the data you want:
public class ResourceAction
{
public int Id {get;set;}
public string Name {get; set; }
}
Select a list of those instead:
List<ResourceAction> actions = resourceActions.Actions
.Select(s => new ResourceAction() { Id = s.Id, Name = s.ActionName}).ToList();
I believe this is what your looking for. However you need to change the output to an anonymous type.
var actions = resourceActions.Actions.Select(s => new { s.ActionName, s.ActionId, s.IsActive } ).ToList();
You can use a anonymous type for this, for example
var actions = resourceActions.Actions.Select(s =>
new { Id = s.Id, Name = s.ActionName, Active = s.IsActive).ToList();
but a better way would be to create a class like
public class ActionWithId
{
public int Id { get; set; }
public string Name { get; set; }
public bool Active { get; set; }
}
List<ActionWithId> actions = resourceActions.Actions.Select(s =>
new ActionWithId() { Id = s.Id, Name = s.ActionName, Active = s.IsActive }).ToList();
Related
I have an one-to-many relation in my entities:
public class Header
{
public Header()
{
Items = new List<Item>
}
public int Id {get; set;}
public virtual ICollection<Item> Items {get; set;}
// other properties
}
public class Item
{
public int Id {get; set;}
public virtual Header Header { get; set; }
public string Title { get; set; }
public DateTime CreationDate { get; set; }
public int Weight { get; set; }
}
I want to load Header and some of its Items, so I wrote this linq to entity query(EF6):
using(var ctx = new MyContext())
{
var result = ctx.Headers.Where(someConditions)
.AsNoTracking()
.Select(header => new {
HeaderId = header.Id,
//fetch other header properties here
LastItemCreationDate = header.Items.OrderByDescending(item => item.CreationDate)
.Select(item => item.Title)
.FirstOrDefault(),
LastItemTitle = header.Items.OrderByDescending(item => item.CreationDate)
.Select(item => item.CreationDate)
.FirstOrDefault(),
LastItemWeight = header.Items.OrderByDescending(item => item.CreationDate)
.Select(item => item.Weight)
.FirstOrDefault()
}).ToList();
}
This query generate a sql script with 3 times join Header and Item tables, is there any more efficent way to write this query to join Header and Item tables one time?
Since you are using Select, you don't need AsNoTracking since the resulting query will not load any entities. The key performance impacts in your case would be indexes in the Header table suitability for your Where clause, then also whether there is a Descending Index available on the CreationDate in the Items table.
Another improvement would be to alter the projection slightly:
var result = ctx.Headers.Where(someConditions)
.Select(header => new {
HeaderId = header.Id,
LatestItem = header.Items
.OrderByDescending(item => item.CreatedDate)
.Select(item => new
{
Title = item.Title,
CreationDate = item.CreationDate,
Weight = item.Weight
}).FirstOrDefault()
}).ToList();
This will change the resulting anonymous type structure a bit, but should result in a nicer, single join.
You will get a result.HeaderId, then a null-able result.LastestItem containing the latest item's properties. So result.LatestItem?.Title instead of result.Title.
Using EF Core code-first, and I want to find any record with a similar list of a foreign entities to the entity I already have.
public class ClownModel {
public int Id { get; set; }
public List<CarModel> Cars { get; set; }
}
public class CarModel {
public int Id { get; set; }
}
var MyClown = new ClownModel() { /*add properties*/ }
//or maybe an existing record selected from database, just some ClownModel instance
Basically, "Select all the ClownModels where they have any Cars.Id that are in my MyClown.Cars"
Assuming that ClownModel has unique CarModel Id's, you can use the following query:
Matches All Ids
var ids = MyClown.Cars.Select(c => c.Id).ToList();
var query =
from cm in ctx.ClownModel
where cm.Cars.Where(c => ids.Contains(c.Id)).Count() == ids.Count
select cm;
Matches Any Ids
var ids = MyClown.Cars.Select(c => c.Id).ToList();
var query =
from cm in ctx.ClownModel
where cm.Cars.Where(c => ids.Contains(c.Id)).Any()
select cm;
LINQ Query not populating
Model extract is as follows
public class ServiceBulletin
{
[Key]
public int Id { get; set; }
public virtual ICollection<ServiceBulletinProducts> ApplicableProducts { get; set; }
}
public class ServiceBulletinProducts
{
[Key]
public int Id { get; set; }
public int ServiceBulletinId { get; set; }
public virtual Product Product{ get; set; }
}
I'm using the following code at the moment to populate a collection
var x = from m in _dc.ServiceBulletins.Include(p => p.ApplicableProducts)
.Include(m => m.Manufacturer)
where m.DeleteStatus == DeleteStatus.Active
select m;
var x1 = new List<ServiceBulletin>();
foreach (var item in x)
{
var p = from m1 in _dc.ServiceBulletinsProducts.Include(p2=>p2.Product)
where m1.Product.DeleteStatus == DeleteStatus.Active &&
m1.ServiceBulletinId == item.Id
select m1;
var p99 = p.ToList();
item.ApplicableProducts = p99;
x1.Add(item);
};
So this is intended to have a Parent Child relationship and I’m trying to do a query which populates a collection of ServiceBulletins with a ApplicableProducts item with a fully populated collection of ServiceBulletinProducts for the ServiceBulletin with the values of the Product populated
The collection is populated but the ServiceBulletinProducts are always set to null and I can’t seem to add an Include such as .Include(p => p.ApplicableProducts.Products) to try and populate the product details – which is resulting in me iterating around the collection to populate the items.
Am I missing something to enable the population on the 1st query for the Include statement or do I need to do the query in a different way ?
Figured out the following should do the trick.
var x = from m in _dc.ServiceBulletins.Include(p => p.ApplicableProducts.Select(p2=>p2.Product))
.Include(m => m.Manufacturer)
where m.DeleteStatus == DeleteStatus.Active
select m;
As you can see, I got this error when I built Data Gird using Kendo UI. Does anybody could point out where I'm wrong in my code below.
private IEnumerable<Product> GetSubProduct()
{
var context = new AdvenDBEntities();
var subcate = context.Products.Select(p => new Product
{
ProductID = p.ProductID,
Name = p.Name,
Color = p.Color,
ListPrice = p.ListPrice,
}).ToList();
return subcate;
}
Error:
The entity or complex type 'AdventureWorks2012Model.Product' cannot be constructed in a LINQ to Entities query.
Thank you so much for your time!
Since Product is an entity of model, you are creating new object of this entity while selecting the records, which is NOT good idea, I am NOT sure how model will handle this kind of behaviour that is why it is preventing you to do so, (I guess). Anyway you can change the code to this,
private IEnumerable<Product> GetSubProduct()
{
var context = new AdvenDBEntities();
var subcate = context.Products.ToList();
return subcate;
}
BTW your function name indicating that you are missing a Where clause.
Also you can create some custom DTO class and use it instead.
E.g.
class ProductDTO
{
public int ProductID { get; set; }
public string Name { get; set; }
public string Color { get; set; }
public decimal ListPrice { get; set; }
}
private IEnumerable<ProductDTO> GetSubProduct()
{
var context = new AdvenDBEntities();
var subcate = context.Products.Select(p => new ProductDTO
{
ProductID = p.ProductID,
Name = p.Name,
Color = p.Color,
ListPrice = p.ListPrice,
}).ToList();
return subcate;
}
The first bad smell code I can point out for you. DBContext implements IDisposable so you are responsible for calling Dispose on it. In all, but one case in here, using block
You must build query to get all the product and then extract from it.
private IEnumerable<Product> GetSubProduct()
{
using (var context = new AdvenDBEntities())
{
// Get all constructed type product and then select from it
var subcate = context.Products
.ToList()
.Select(p => new Product
{
ProductID = p.ProductID,
Name = p.Name,
Color = p.Color,
ListPrice = p.ListPrice,
});
return subcate;
}
}
Be first, my English is not very good. So I am sorry about that. :)
My question as the title. I have two tables on my database:
Siniflar (SinifId, SinifAdi, Kapasite, OgretmenId)
Ogretmenler (OgretmenId, Ad, Soyad, Brans)
Query:
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new { s.SinifId, s.SinifAdi, s.Kapasite, o.Ad }).ToList();
I want to use the result of the query as a generic, like this:
public List<Siniflar> SiniflariListele()
{
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new { s.SinifId, s.SinifAdi, s.Kapasite, o.Ad }).ToList();
return siniflar;
}
But I get an error. Because the result is anonymous types.
Error: Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<Entity.Siniflar>
How Can I use be generic result. What Can I do for that?
I changed question:
Class:
public class RSiniflar
{
public int SinifId { get; set; }
public string SinifAdi { get; set; }
public int Kapasite { get; set; }
public string OgretmenAdiSoyadi { get; set; }
}
Metod:
public List<RSiniflar> SiniflariListele()
{
List<RSiniflar> siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new RSiniflar
{
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite,
OgretmenAdiSoyadi = o.Ad + ' ' + o.Soyad
}).ToList();
return siniflar;
}
But now error to query: Unable to create a constant value of type 'System.Object'. Only primitive types or enumeration types are supported in this context.
I think, there are a problem on my query... I get an error same when query to var type...
You can return typed list, but you can't return a list of anonymous type. So you need to create a class which will handle your results:
public class A
{
public int SinifId { get; set; }
public int SiniAdi { get; set; }
public int Kapasite { get; set; }
public int Ad { get; set; }
}
And then use it in your query, instead of anonymous objects:
public List<A> SiniflariListele()
{
var siniflar = (from s in db.Siniflar
join o in db.Ogretmenler
on s.OgretmenId equals o.OgretmenId
select new A {
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite,
Ad = o.Ad
}).ToList();
return siniflar;
}
You could do the same with an existing class (e.g. Siniflar), but you have to be sure that this class has all necessary properties.
Rather than using new { property1, property2 }, create new Siniflar's in your select.
E.g.
select new Siniflar() {
SinifId = s.SinifId,
SinifAdi = s.SinifAdi,
Kapasite = s.Kapasite }).ToList()
Note: as lazyberezovsky mentioned, your mapping seems to be flawed, as Siniflar does not contain the property Ad.