I am querying a table resulting from two other tables in the image below.
In one category I can have several questions.
using this query did not have the result I expected:
var result = await _repository.GetQuestionCategory()
.Include(x => x.Category)
.Include(y => y.Question)
.Select(x => new QuestionCategoryViewModel
{
Id = x.Id,
CategoryId = x.Category.Id,
CategoryName = x.Category.Name,
IsRequired = x.IsRequired,
QuestionId = x.Question.Id,
QuestionName = x.Question.Name,
Weigth = x.Weigth
}).GroupBy(x => x.CategoryId).ToListAsync().ConfigureAwait(false);
How could I send a similar structure like this
{ categoryId, categoryName, IsRiquered, Weigth, questions: [ questionId: questionName: y]}
Mmodel Category and Question
public class QuestionCategory
{
public Guid Id { get; set; }
public Question Question { get; set;}
public Category Category { get; set;}
public int QuestionId { get; set; }
public int CategoryId { get; set; }
public bool IsRequired { get; set; }
public int Weigth { get; set; }
}
You should use a GroupBy statement with most of its parameters. Note the inconsistent naming of the result properties is taken 1:1 from the question. You may want to create some explicit DTO type instead of creating the result as anonymous type.
IQueryable<QuestionCategory> questionCategories = new EnumerableQuery<QuestionCategory>(Enumerable.Empty<QuestionCategory>());
var result = questionCategories.GroupBy(
// key selector
qc => new
{
categoryId = qc.CategoryId,
categoryName = qc.Category.Name,
IsRiquered = qc.IsRequired,
Weigth = qc.Weigth
},
// element selector
qc => qc.Question,
// result selector
(k, v) => new
{
k.categoryId,
k.categoryName,
k.IsRiquered,
k.Weigth,
questions = v.Select(q => new {questionId = q.Id, questionName = q.Name}).ToList()
});
Related
I have the following query:
var catInclude = _db.Cat
.Where(x => x.ProvId == request.ProvId)
.Include(x => x.CatItems)
.SingleOrDefault(p => p.Id == request.ProvId
cancellationToken: cancellationToken);
As I don't want to get all properties from CatItems with Include(), I have created the following query:
var catSelect = _db.Cat
.Where(x => x.ProvId == request.ProvId)
.Select(p ==> new
{ Provider = p,
Items = p.CatItems.Select(x => new List<CatItems> { new CatItems
{ Id = x.Id, Name = x.Name, Price = x.Price } }
})})
SingleOrDefault(cancellationToken: cancellationToken);
But something is wrong in the 2nd query because here return _mapper.ProjectTo<CatDto>(cat) I get the following error:
Argument 1: cannot convert from '<anonymous type: Db.Entities.Cat Prov, System.Colletions.Generic.IEnumerable<System.Colletions.Generic.List<Models.CatItems> > Items>' to 'System.Linq.IQueryable'
Here is my CatDto:
public class CatDto
{
public int ProvId { get; set; }
public List<CatItems> CatItems { get; set; }
}
Here are my entities:
public class Prov
{
public int Id { get; set; }
public Cat Cat { get; set; }
}
public class Cat
{
public int Id { get; set; }
public int ProvId { get; set; }
public List<CatItems> CatItems { get; set; }
}
public class CatItems
{
public int Id { get; set; }
public int CatId { get; set; }
public DateTime CreatedOn { get; set; }
}
Is there a way to recreate the 2nd query and use it?
Main difference that instead of returning List of CatItems, your code returns IEnumerable<List<CatItems>> for property Items.
So, just correct your query to project to List:
var catSelect = await _db.Cat
.Where(x => x.ProvId == request.ProvId)
.Select(p => new CatDto
{
ProvId = p.ProvId,
Items = p.CatItems.Select(x => new CatItems
{
Id = x.Id,
Name = x.Name,
Price = x.Price
})
.ToList()
})
.SingleOrDefaultAsync(cancellationToken: cancellationToken);
I mean, even the exception is pretty self-explanatory. Nevertheless:
You are performing a .Select(...). It returns an Anonymous type. So, your catSelect is an anonymous type, thus the AutoMapper fails.
The quickest fix is to just cast (Cat)catSelect before mapping.
Or, you can dig deeper into how does AutoMapper play with anonymous types.
I feel like you can make most of the classes inherent Id and why is public cat CAT {get; set;} i thought you were supposed to initialize some kind of value
I need to write some dynamic select expression on entity framework something like in the example.
var list = db.Article
.GroupBy(x => x.CategoryId)
.Select(x => new ArtDto
{
No = x.Select(c => c.NUMBER).FirstOrDefault(),
UserName = x.Key,
Count = x.Count()
})
.ToList();
I can write group by with expression like this:
Expression<Func<Article, int>> groupByExp;
groupByExp = (x) => x.CategoryId;
So I can replace actual expression with groupByExp.
var list = db.Article
.GroupBy(groupByExp)
.Select(x => new ArtDto
{
No = x.Select(c => c.NUMBER).FirstOrDefault(),
UserName = x.Key,
Count = x.Count()
})
.ToList();
I also want to write another expression for select. So I can send it to another function and it will be dynamic on that function.
Expression<Func<Article, bool>> selectExp;
selectExp = (x) => new ArtDto { ... };
Is it possible? Do you have any idea or tutorial for that?
Yes it is possible,
before start you need to:
Create the new object for selected properties
Map your model to the new object
lets consider that you have your model Article and you need to return the new model ArticleSummary as below
public class Article {
public int id { get; set; }
public string Title { get; set; }
public string Introduction { get; set; }
public string AuthorId { get; set; }
public AppUser Author { get; set; }
public DateTime PublishDate { get; set; }
}
public class ArticleSummary {
public int Id { get; set; }
public string Title { get; set; }
public string Introduction { get; set; }
}
and here is the mapping :
Expression<Func<Article, ArticleSummary>> mapArticle = x => new ArticleSummary {
Id = x.Id,
Title = x.Title,
Introduction = x.Introduction
};
and here is the "simplified" data function :
// T is Article model
// U is ArticleSummary model
public async Task<ICollection<U>> SelectListAsync<T, U>(
Expression<Func<T, bool>> search,
Expression<Func<T, U>> select) where T : class
{
var query =
_context.Set<T>()
.Where(search)
.Select(select);
return await query.ToListAsync();
}
you can call it by passing mapping expression to select property.
Your expression should take IIGrouping<T, Article> as first argument (where T is a type of CategoryId). Assuming that CategoryId is int expression can be written like
public static Expression<Func<IGrouping<int, Article>, ArtDto>> SelectExpression()
{
return x => new ArtDto
{
No = x.Select(c => c.NUMBER).FirstOrDefault(),
UserName = x.Key,
Count = x.Count()
};
}
I have a use-case with a deeply nested class hierarchy, for example like this:
public class Parent
{
public int Id { get; set; }
public List<ChildOne> Children { get; set; }
}
public class ChildOne
{
public int Id { get; set; }
public int ParentId { get; set; }
public List<ChildTwo> ChildrenTwo { get; set; }
}
public class ChildTwo
{
public int Id { get; set; }
public int Priority { get; set; }
public int ChildOneId { get; set; }
public List<ChildThree> ChildrenThree { get; set; }
}
public class ChildThree
{
public int Id { get; set; }
public int ChildTwoId { get; set; }
}
If I want to load all parent-objects and their related children levels, I'd do this:
var objects = context.Parent
.Include(parent => parent.Children)
.ThenInclude(childOne => childOne.ChildrenTwo)
.ThenInclude(childTwo => childTwo.ChildrenThree)
.ToList();
But what if I want my ChildrenTwo entities in the eager-loaded navigational property of ChildOne to be ordered by their Priority? I've done some research, and from the links below (and some others), it is apparently not directly possible in EF Core (yet):
https://github.com/aspnet/EntityFrameworkCore/issues/9445
https://github.com/aspnet/EntityFrameworkCore/issues/2919
https://github.com/aspnet/EntityFrameworkCore/issues/9067
So, how can you achieve the ordering of the ChildrenTwo above (by Priority) in a good/clean way that is fast? That probably means most of the work should happen on the DB server and not on the .NET client side. What's the best approach here?
Though it is very late to answer, but it may help the future readers:
I will explain the code:
var authorArticles = await _context.AuthorArticles
.Include(a => a.Author)
.ThenInclude(p => p.Person)
.ThenInclude(pq => pq.Qualifications)
.ThenInclude(q => q.QualificationSubject)
.Include(a => a.Author)
.ThenInclude(p => p.Person)
.ThenInclude(pp => pp.Professions)
.Include(a => a.Author)
.ThenInclude(p => p.Person)
.ThenInclude(pp => pp.Professions)
.ThenInclude(prof => prof.Profession)
.Where(aa => aa.ArticleId == articleId)
.Select(s => new AuthorArticle
{
Author = new Author
{
Affiliation = s.Author.Affiliation,
AvailableAsReviewer = s.Author.AvailableAsReviewer,
Person = new Person
{
Email = s.Author.Person.Email,
FirstName = s.Author.Person.FirstName,
LastName = s.Author.Person.LastName,
MiddleName = s.Author.Person.MiddleName,
Title = s.Author.Person.Title,
FullName = s.Author.Person.FullName,
UserId = s.Author.Person.UserId,
Professions = new Collection<PersonProfession>
{
new PersonProfession
{
// using sorting here!!
Organization = s.Author.Person.Professions
.OrderByDescending(pid => pid.ProfessionId)
.FirstOrDefault().Organization,
Profession = s.Author.Person.Professions
.OrderByDescending(pid => pid.ProfessionId)
.FirstOrDefault().Profession
}
},
Qualifications = new Collection<PersonQualification>
{
new PersonQualification
{
QualificationSubject = s.Author.Person.Qualifications
.OrderByDescending(q => q.QualificationLevelId)
.FirstOrDefault().QualificationSubject,
QualificationLevelId = s.Author.Person.Qualifications
.OrderByDescending(q => q.QualificationLevelId)
.FirstOrDefault().QualificationLevelId
}
}
}
},
IsCorresponding = s.IsCorresponding,
AuthorPosition = s.AuthorPosition
}).ToListAsync();
return authorArticles;
If you simply eager loaded the entities, then at the time of projection; which means when you are selecting the items from the query, you can recreate the object that has already been provided in slightly different way. In my case, I wanted only one profession of the person out of many and same goes for the qualification of the person.
Took help of select from Another SO great answer!
I'm using jqueryui autocomplete to assist user in an item selection. I'm having trouble selecting the correct items from the objects' subcollections.
Object structure (simplified) is
public class TargetType
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<SubCategory> SubCategories { get; set; }
public TargetType()
{
SubCategories = new HashSet<SubCategory>();
}
}
public class SubCategory
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<SubTargetType> SubTargetTypes { get; set; }
public SubCategory()
{
SubTargetTypes = new HashSet<SubTargetType>();
}
}
Currently I'm doing this with nested foreach loops, but is there a better way?
Current code:
List<SubTargetResponse> result = new List<SubTargetResponse>();
foreach (SubCategory sc in myTargetType.SubCategories)
{
foreach (SubTargetType stt in sc.SubTargetTypes)
{
if (stt.Name.ToLower().Contains(type.ToLower()))
{
result.Add(new SubTargetResponse {
Id = stt.Id,
CategoryId = sc.Id,
Name = stt.Name });
}
}
}
You can do using Linq like this
var result = myTargetType.SubCategories
.SelectMany(sc => sc.SubTargetTypes)
.Where(stt => stt.Name.ToLower().Contains(type.ToLower()))
.Select(stt => new SubTargetResponse {
Id = stt.Id,
CategoryId = sc.Id,
Name = stt.Name });
The above query doesn't work. The following should work, but I'd not recommend that as that'd not be faster or more readable.
var result = myTargetType.SubCategories
.Select(sc => new Tuple<int, IEnumerable<SubTargetType>>
(sc.Id,
sc.SubTargetTypes.Where(stt => stt.Name.ToLower().Contains(type.ToLower()))))
.SelectMany(tpl => tpl.Item2.Select(stt => new SubTargetResponse {
Id = stt.Id,
CategoryId = tpl.Item1,
Name = stt.Name }));
Actually there are 2 different questions.
LINQ select all items of all subcollections that contain a string
Solutions:
(A) LINQ syntax:
var result =
(from sc in myTargetType.SubCategories
from stt in sc.SubTargetTypes.Where(t => t.Name.ToLower().Contains(type.ToLower()))
select new SubTargetResponse
{
Id = stt.Id,
CategoryId = sc.Id,
Name = stt.Name
})
.ToList();
(B) Method syntax:
var result =
myTargetType.SubCategories.SelectMany(
sc => sc.SubTargetTypes.Where(stt => stt.Name.ToLower().Contains(type.ToLower())),
(sc, stt) => new SubTargetResponse
{
Id = stt.Id,
CategoryId = sc.Id,
Name = stt.Name
})
.ToList();
Currently I'm doing this with nested foreach loops, but is there a better way?
Well, it depends of what do you mean by "better". Compare your code with LINQ solutions and answer the question. I personally do not see LINQ being better in this case (except no curly braces and different indentation, but a lot of a hidden garbage), and what to say about the second LINQ version in this answer - if that's "better" than your code, I don't know where are we going.
I have two classes:
public class Topic
{
public Topic()
{
this.SubTopics = new HashSet<SubTopic>();
}
public int TopicId { get; set; }
public string Name { get; set; }
public virtual ICollection<SubTopic> SubTopics { get; set; }
}
public class SubTopic
public int SubTopicId { get; set; }
public int Number { get; set; }
public int TopicId { get; set; }
public string Name { get; set; }
public virtual Topic Topic { get; set; }
}
What I would like to do is to get a Data Transfer Object output from LINQ that will show me. I do want to see the TopicId repeated if there is more than one SubTopic inside that topic:
TopicId Name SubTopicId Name
1 Topic1 1 SubTopic1
1 Topic1 2 SubTopic2
1 Topic1 3 SubTopic3
2 Topic2 4 SubTopic4
I tried to code a Linq statement like this:
var r = context.Topics
.Select ( s => new {
id = s.TopicId,
name = s.Name,
sid = s.SubTopics.Select( st => st.SubTopicId),
sidname = s.SubTopics.Select ( st => st.Name)
}).
ToList();
But this does not really work as it returns sid and sidname as lists.
How will it be possible for me to get a flat output showing what I need?
You need SelectMany to expand a nested collection, along these lines
var r = context.Topics.SelectMany(t => t.SubTopics
.Select(st => new
{
TopicID = t.TopicId,
TopicName = t.Name,
SubTopicID = st.SubTopicId,
SubTopicName = st.Name
}));
try this :
var r = context.Topics
.Select ( s => new {
id = s.TopicId,
name = s.Name,
sid = s.SubTopics.Where(st=>st.TopicId==s.TopicId).Select( st => st.SubTopicId ),
sidname = s.SubTopics..Where(st=>st.TopicId==s.TopicId).Select ( st => st.Name)
}).
ToList();
Hope it will help
#Sweko provided an answer that satisfies the exact output that you requested. However, this can be even simpler if you just return the subtopic intact. It may run a bit quicker as well, since you don't need to create a new object for each element in the result.
Lastly, it looks like you wanted your result set ordered. For completeness, I've added those clauses as well.
var r = context.Topics
.SelectMany( topic => topic.SubTopics )
.OrderBy(sub => sub.TopicId)
.ThenBy(sub => sub.SubTopicId);