I am having 2 entities as described below
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Comment> Comments { get; set; }
}
public class Comment
{
public int Id { get; set; }
public string Message { get; set; }
[ForeignKey("Product")]
public int ProductId { get; set; }
public Product Product { get; set; }
}
Now I want to write a query which includes only 10 comments for a particular product. The query i have written below includes all comments on product.
var product = db.Products.Include(a=>a.Comments).Take(10);
Please suggest is it possible in entity framework.
Edit 1
changed this query to
var product = db.Products.Include(a=>a.Comments).FirstOrDefault(c=>c.Id==1);
this one
var product = db.Products.Include(a=>a.Comments).Take(10);
I have to load 10 products with 10 comments each.
you can always reverse that and get the Comments with the product:
var comments = db.Comments.Include(c => c.Product)
.Where(c => c.Product.Id == 1)
.Take(10);
This will work if you don't mind returning an anonymous type or a poco:
var products = from x in db.Products.Take(10)
select new
{
ProductProperty1 = x.Property1,
Comments = x.Comments.Take(10),
};
var product = products.FirstOrDefault(c=>c.ProductProperty1 ==1);
I believe that following will do:
var comments = db.Comments.Where(c=>c.ProductId==1).Take(10).ToList();
var product = db.Products.FirstOrDefault(c=>c.Id==1);
Related
I search for a way to combine two or more IQueryables from different Object types in order to use it as a datasource for my treelist.
For the treelist I use the DevExpress WinForms component "TreeList".
It provides me the properties "KeyFieldName" which is usually mapped to the "ID" and the ParentFieldName which is mapped to the parent id in order to build a hierarchy.
I use entity framework 6 as or mapper.
I have the two following classes I would need to combine:
XObject:
[Table("tbl_objects")]
public class XObject
{
[Column("id")]
public int Id { get; set; }
[Column("display_name")]
public String DisplayName { get; set; }
[Column("description")]
public String Description { get; set; }
[Column("usage_reason")]
public String UsageReason { get; set; }
[Column("is_network_compatible")]
public bool IsNetworkCompatible { get; set; }
[Column("ip_address")]
public String IpAddress { get; set; }
[Column("network_name")]
public String NetworkName { get; set; }
[Column("serial_number")]
public String SerialNumber { get; set; }
[Column("manufacturer_identification_code")]
public String ManufacturerIdentificationCode { get; set; }
[Column("web_link")]
public String WebLink { get; set; }
[Column("warranty")]
public int WarrantyInDays { get; set; }
[Column("ref_manufacturer")]
public virtual XManufacturer Manufacturer { get; set; }
[Column("ref_order")]
public virtual XOrder Order { get; set; }
[Column("ref_owner")]
public virtual XOwner Owner { get; set; }
[Column("ref_room")]
public virtual XRoom Room { get; set; }
[Column("ref_object_folder")]
public virtual XObjectFolder ObjectFolder { get; set; }
public virtual ICollection<XAdditionalObjectData> AdditionalObjectData { get; set; }
}
XObjectFolder:
[Table("tbl_object_folders")]
public class XObjectFolder
{
[Column("id")]
public int Id { get; set; }
[Column("display_name")]
public String DisplayName { get; set; }
[Column("short_name")]
public String ShortName { get; set; }
[Column("ref_parent_folder")]
public virtual XObjectFolder ParentFolder { get; set; }
public virtual ICollection<XObjectFolder> ChildFolders { get; set; }
public virtual ICollection<XObject> Objects { get; set; }
[NotMapped]
public int ParentFolderId { get { return ParentFolder == null ? -1 : ParentFolder.Id; } }
}
As you've probably already seen, an object folder can contain subfolders but also objects.
My goal is to see this as one "datasource" in my treelist.
For example like this:
Object Folder A
Object Sub-Folder A
Object 1
Object 1
In other questions here I've found the possibilities to concat or union queryables, but that only works with them being the same type:
using (var db = new XDbContext(_conString))
{
// Queryables
var ofs = from of in db.ObjectFolders orderby of.DisplayName ascending select of; // <- All ObjectFolders
var obs = from obj in db.Objects orderby obj.DisplayName ascending select obj; // <- All Objects
// Concat them
var comb = ofs.Concat(obs); // <- not the same type
// As DataSource for my TreeList
TreeListObjects.DataSource = comb.ToList();
}
Which is why I am searching for a good way to make this possible.
I could also imagine me using a pretty bad approach to reach my goal. So I am open to suggestions. This is a personal project which I do to improve myself at stuff.
Thanks in advance!
EDIT
So I managed to get a step further by using an interface both classes share:
public interface ITreeListCombinable
{
int Id { get; set; }
int ParentId { get; }
String DisplayName { get; set; }
}
But... who would've thought... there occures another problem:
Have a look at the db structure:
Db_Struture
Since both objects are stored in different tables, the id's will certainly not be unique when combining them.
Which is necessary when setting the datasource.
Solution:
So I've taken my own approach to my problem and it worked out.
Full disclosure -> I consider myself a beginner, so this solution is probably not the best. Still, if anyone is in a similar situation, here's how it could work:
First I created an interface, which both the folder and objects share:
ITreeListCombinable
public interface ITreeListCombinable
{
int Id { get; set; }
int ParentId { get; }
int ListId { get; set; }
int ParentListId { get; set; }
String DisplayName { get; set; }
ObjectTreeListElementTypes TreeListElementType { get; }
}
I then made sure, both my XObject and XObjectFolder classes held the ObjectTreeListElementTypes value they're corresponding to:
ObjectTreeListElementTypes Enum:
public enum ObjectTreeListElementTypes
{
Folder,
Object
}
Classes:
[NotMapped]
public ObjectTreeListElementTypes TreeListElementType => ObjectTreeListElementTypes.Folder; // or *.Object for that matter
So afterwards I've wrote my own "controller" which handles my specific scenario.
ObjectTreeListElementController:
public class ObjectTreeListElementController
{
private List<ITreeListCombinable> _list;
public ObjectTreeListElementController()
{
_list = new List<ITreeListCombinable>();
}
public void AddRange(List<ITreeListCombinable> list)
{
// add incoming items to private _list
_list.AddRange(list);
}
public List<ITreeListCombinable> GetDataSourceList()
{
// create auto increment list id
var listId = 0;
foreach (var item in _list)
{
item.ListId = listId;
listId++;
}
// set new parent list id according to incremental list id
foreach (var item in _list)
{
var parents = _list.Where(x => x.Id == item.ParentId && x.TreeListElementType == ObjectTreeListElementTypes.Folder);
if (parents.Count() > 0)
item.ParentListId = parents.First().ListId;
else
item.ParentListId = -1;
}
return _list;
}
}
Essentially, when calling the GetDataSourceList() method, it firstly distributes incremental, temporary list-ids.
In a second loop I then search for the original parent id and match the tree list element type. If none is found, this folder is a root folder in my treelist, if one is found, the given list-id becomes the parent list id:
using (var db = new XDbContext(_conString))
{
// Queryables
IQueryable<ITreeListCombinable> ofs = from of in db.ObjectFolders orderby of.DisplayName ascending select of;
IQueryable<ITreeListCombinable> objs = from obj in db.Objects orderby obj.DisplayName ascending select obj;
var lofs = ofs.ToList();
var lobjs = objs.ToList();
var ctrl = new ObjectTreeListElementController();
ctrl.AddRange(lofs);
ctrl.AddRange(lobjs);
var sourceList = ctrl.GetDataSourceList();
// As DataSource for my TreeList
TreeListObjects.DataSource = sourceList;
}
And this brought me the exact output I've wanted:
Hope this helps another beginner :)
In the following example in Entity Framework, how to find the author of a specified book using linq:
public class Author
{
public int Id { get; set; }
public string AuthorName { get; set; }
public ICollection<Book> Books { get; set; }
}
public class Book
{
public int Id { get; set; }
public int Title { get; set; }
}
Thanks.
Assuming you have a collection of authors, you would simply do
var author = authors.SingleOrDefault(x=> x.Books.Any(y=> y.Title.Equals(bookTitle, StringComparison.OrdinalIgnoreCase))
This assumes that books have only one author.
You can achieve it in this simple way, Demo on dotnetfiddle
var result = authors.SelectMany(a => a.Books.Select(b => new { BookTitle = b.Title, AuthorName = a.AuthorName }));
I have next entity
public class Objective
{
public virtual UserInfo AssignedUser { get; set; }
public int? AssignedUserID { get; set; }
public string ObjectiveText { get; set; }
public virtual ICollection<ObjectiveTask> Tasks { get; set; }
public virtual UserInfo User { get; set; }
public int UserID { get; set; }
}
One objective could has one Assigned User and one User but many Tasks.
After getting Entity from DB I map it to DTO class which looks like this
public class ObjectiveListViewModel
{
public string AssignedString { get; set; }
public string ObjectiveText { get; set; }
public int TasksCount { get; set; }
public string UserContactName { get; set; }
}
Mapping settings doesn't meter
When I do this with query like this
(from objective in context.Set<Objective>() select objective)
.Include(o => o.User)
.Include(o => o.AssignedUser)
.ToListAsync();
Everything works cool - User and Assigned User properties are loaded and no need do extra query to DB to get their data.
But I need return objectives with tasks amount.
To do this I've created a generic class
public class EntitySubCount<TEntity>
{
public TEntity Entity { get; set; }
public int GroupCount { get; set; }
}
And use it in this way
(from objective in context.Set<Objective>() select objective)
.Include(o => o.User)
.Include(o => o.AssignedUser)
.Select(o=> new EntitySubCount<Objective> {
Entity = o,
GroupCount = o.Tasks.Count })
.ToListAsync();
But User and Assigned User properties are not loaded and it require additional query to DB to get their data.
I understand that it because lazy loading.
The question is - how I can get from DB my Entity with loaded nav. properties and with count of Tasks at once?
Thank you for any help
You are close. No need for the includes if you are projecting. In this case I project to an anonymous type, but you could create a ViewModel class to project to if desired.
var objectiveList = context.Objectives
.Select(o => new
{
Entity = o,
// or you could just pick the properties:
ObjectiveText = o.ObjectiveText,
User = o.User,
AssignedUser = o.AssignedUser,
GroupCount = o.Tasks.Count
}).ToList();
EDIT: I see you already have a ViewModel(DTO). You might be looking for something like this:
var objectiveList = context.Objectives
.Select(o => new ObjectiveListViewModel
{
AssignedString = o.AssignedUser.Name,
ObjectiveText = o.ObjectiveText,
TasksCount = o.Tasks.Count
UserContactName = o.User.Name
}).ToList();
Database Models of my Application are:
public class Restaurant
{
public int Id { get; set; }
.........
}
public class Review
{
public int Id { get; set; }
public string ReviewTitle { get; set; }
public string ReviewContent { get; set; }
public int UserId { get; set; }
public int RestaurantId { get; set; }
}
public ReviewHelpful
{
public int Id { get; set; }
public int ReviewId { get; set; }
public bool IsHelpfull { get; set; }
}
public ReviewImage
{
public int Id { get; set; }
public string ImageLink { get; set; }
public int ReviewId { get; set; }
}
There is no navigation property in any table. In ReviewHelpful table, If user finds helpfull of this review than value is true otherwise false.
Now I want to create a view-model Like this:
public class ReviewViewModel
{
public int ReviewId { get; set; }
public int RestaurantId { get; set; }
public string ReviewTitle { get; set; }
public string ReviewContent { get; set; }
public int UserId { get; set; }
public int NumberOfHelpfull { get; set; }
public int NumberOfNotHelpfull { get; set; }
public List<string> ImagesLinks { get; set; }
}
For that reason, I want to write this kind of query :
var reviews = (from review in _foodTrackerContext.RestaurantReviews
join helpful in _foodTrackerContext.Helpfuls on review.Id equals helpful.ReviewId
join reviewPicture in _foodTrackerContext.ReviewPictures on review.Id equals reviewPicture.ReviewId
where review.ResturantId == 2
select new ReviewViewModel()
{
Id = review.Id,
RestaurantId = 2,
ReviewTitle = review.ReviewTitle,
ReviewContent = review.ReviewContent,
NumberOfHelpfull = .. ??,
NumberOfNotHelpfull = ... ??,
ImagesLinks = ... ???
}
I can not retrieve HelpfulYes, HelpfulNo, ImagesLinks with this query. What would be query for finding these variables?.
This query produces multiple rows for single review with each ReviewImage and each ReviewHelpful.
The query that ypu need to do is this one:
var model =
from review in ctx.Reviews
where review.RestaurantId == 2
join helpful in ctx.ReviewHelpfuls
on review.Id equals helpful.ReviewId into helpfuls
join image in ctx.ReviewImages
on review.Id equals image.ReviewId into images
select new RestaurantReviewViewModel
{
Id = review.Id,
RestaurantId = 2,
ReviewTitle = review.ReviewTitle,
ReviewContent = review.ReviewContent,
NumberOfHelpfull = helpfuls.Count(h => h.IsHelpfull),
NumberOfNotHelpfull = helpfuls.Count(h => !h.IsHelpfull),
ImagesLinks = (from image in images select image.ImageLink).ToList()
};
Please, note that when you do a one to manyh join you need to include an into to give a nameto the joined entities to be able to work on them.
I've used the dot syntax for selecting the count, but you could use the query syntax if you wanted. Over time, I've found dot synatx more natural.
NOTE: if you used navigation properties this would become much easier. Why are you not using them? With navigation properties you don't need to make the joins explicitly, as they are already available.
List<ReviewViewModel> listModel = new List<ReviewViewModel>();
context.dbRestaurant
.include("Review")
.include("Review.ReviewHelpful")
.include("Review.ReviewImage").ToList().ForEach((item) =>
{
ReviewViewModel model = new ReviewViewModel();
model.ID = item.ID
listModel.Add(model);
});
Given the (simplified) object model below, I need to load the Schedule object that corresponds to a given Person, but only load select Classes that the person is taking.
I'm accomplishing that using a projection and it works fine (except for EF Profiler complaining about too many joins).
Now I have a new requirement to also load Person.FunFacts. I hoped the commented-out code //FunFacts = s.Person.FunFacts, would accomplish that. However, it does not.
I can accomplish my goal by accessing schedule.FunFacts while the context is still active. However, that creates an additional round trip to the database.
Question: Can I modify my projection to return schedule.FunFacts without resorting to lazy loading it via the proxy?
Object Model (simplified)
public class Schedule
{
public int Id { get; set; }
public Person Person { get; set; }
public List<Class> Classes { get; set; }
}
public class Class
{
public int Id { get; set; }
public int Name { get; set; }
}
public class Person
{
public int Id { get; set; }
public Schedule Schedule { get; set; }
public List<FunFact> FunFacts { get; set; }
}
public class FunFact
{
public int Id { get; set; }
public string Name { get; set; }
public string Text { get; set; }
}
Materialization Code
var desiredPersonId = 42;
var classIds = new List<int> { 2, 3, 5, 7, 11 };
var schedule = (from sFilter in
(from s in ctx.Schedules
where s.Person.Id == desiredPersonId
select new
{
Schedule = s,
Person = s.Person,
//FunFacts = s.Person.FunFacts,
Class = from c in s.Classes where classIds.Contains(c.Id) select c
}
).AsEnumerable()
select sFilter.Schedule).FirstOrDefault();
It turns out that FunFacts is indeed selected, just not related to the instance of Schedule.
Inspired by an article, I resolved the issue by making the following changes:
var scheduleProjection =
(from s in ctx.Schedules
where s.Person.Id == desiredPersonId
select new
{
Schedule = s,
Person = s.Person,
FunFacts = s.Person.FunFacts,
Class = from c in s.Classes where classIds.Contains(c.Id) select c
}
).FirstOrDefault();
var schedule = scheduleProjection.Schedule;
schedule.FunFacts = scheduleProjection.FunFacts;