I'm working on kind of education project (for myself) to learn EF Core -> code first approach and I'm struggling what is wrong with my query. A have two simple entitities: article, and user and I want to group them to get an list of objects that contain list of all user with related articles.
{
var authorRowModels =
from articles in _myContext.Articles
join authors in _myContext.Users on articles.Author.Id equals authors.Id
group new { articles, authors } by authors into authorWithArticles
select new
{
AuthorFirstName = authorWithArticles.Key.FirstName,
AuthorLastName = authorWithArticles.Key.LastName,
Articles = authorWithArticles.Select(x => x.articles)
};
return View(authorRowModels.AsEnumerable().Select(x => new AuthorRowModel
{
AuthorFirstName = x.AuthorFirstName,
AuthorLastName = x.AuthorLastName,
Articles = x.Articles.ToList()
}));
}
but I'm getting an error:
InvalidOperationException: The LINQ expression 'DbSet .LeftJoin( outer: DbSet, inner: a => EF.Property<Nullable>(a, "AuthorId"), outerKeySelector: u0 => EF.Property<Nullable>(u0, "Id"), innerKeySelector: (o, i) => new TransparentIdentifier<Article, User>( Outer = o, Inner = i )) .Join( outer: DbSet, inner: a => a.Inner.Id, outerKeySelector: u => u.Id, innerKeySelector: (a, u) => new TransparentIdentifier<TransparentIdentifier<Article, User>, User>( Outer = a, Inner = u )) .GroupBy( source: ti => ti.Inner, keySelector: ti => new { articles = ti.Outer.Outer, authors = ti.Inner })' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
and I have no idea what EF not able to translate. Also if you have a hint how to rewrite this query in better way maybe even without grouping it'd be great :)
Thank you.
Using join in EF LINQ is almost always the wrong solution.
With a Navigation Property this can simply be something like:
var authorRowModels = from a in _myContext.Users
where a.Articles.Any()
select new
{
a.FirstName,
a.LastName,
a.Articles
};
Related
I have entities like Product(Id, Name) and Keyword(Id, Description), and there is a many-to-many relationship between them.
The essence of my task is the following, I need to do a full-text search on Name and Description columns, using EF CORE 6
I already have some SQL code that works fine.
SELECT a."Id", a."Name" as name, k.txt
FROM "Products" AS a
LEFT JOIN (
SELECT x."ProductsId" as Id, string_agg(y."Description", ' ') as txt
FROM "ProductKeywords" x
JOIN "Keywords" y ON y."Id" = x."KeywordId"
GROUP BY 1
) k ON a."Id" = k.Id
WHERE to_tsvector(concat_ws(' ', a."Name", k.txt))
## to_tsquery('Some text');
And I need to write some LINQ code that will do something similar, but I have a problem with string_agg, and I don't understand how to implement it in LINQ and EF CORE will reflect it correctly
I tried to do the following
var products = _context.Products
.Select(e => new
{
Id = e.Id,
Name = e.Name,
Keywords = string.Join(" ", e.Keywords.Select(q => q.Description))
}).Where(e => EF.Functions.ToTsVector(e.Keywords).Matches("Some text")).ToList();
But I get an error, and it's most likely because of string.Join
could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'
Got the result, using linq2db
var query = _context.Products.ToLinqToDB()
.LeftJoin(_context.ProductsKeywords.ToLinqToDB().GroupBy(r => r.ProductId).Select(e => new {
Key = e.Key,
Txt = e.StringAggregate(",", t => t.Keyword.Description).ToValue()
}),
(product, productKeyword) => product.Id == productKeyword.Key,
(i, j) => new {
Id = i.Id,
Txt = j.Txt
}).Select(e => new {
Id = e.Id,
Txt = EF.Functions.ToTsVector(e.Txt)
}).Where(w => w.Txt.Matches("Some text"));
I updated my .net core 2.2 to 5
I have a error about ef that
System.InvalidOperationException: 'The LINQ expression 'x' could not
be translated. Either rewrite the query in a form that can be
translated, or switch to client evaluation explicitly by inserting a
call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or
'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for
more information.'
public List<CustomerPageModel> GetCustomers(int AccountID)
{
return (from p in context.Customers
join f in context.Patients on p.ID equals f.CustomerID into ps
from t in ps.DefaultIfEmpty()
where p.AccountID == AccountID
select new CustomerPageModel
{
ID = p.ID,
Name = p.Name,
IsActive = p.IsActive,
TC = p.TC,
Surname = p.Surname,
Email = p.Email,
Address = p.Address,
Phone = p.Phone,
Note = p.Note,
AccountID = p.AccountID,
Pats = string.Join(",", ps.Select(x => x.Name)),
PatCount = ps.Count()
})
.GroupBy(p => p.ID)
.Select(g => g.First())
.ToList();
}
How can I convert that code?
Your problem line is:
Pats = string.Join(",", ps.Select(x => x.Name)),
Specifically, the string.Join method doesn't translate to SQL, so in previous versions of EF, it had to retrieve the data from the database then in-memory preform the string.Join function. Now EF explicitly tells you it can't run that on the database server - this is a breaking change but a design decision that tells you (the developer) that it may not have been running as efficiently as you thought it was...
To "fix" this, and based on your particular code example I'd recommend the following:
Add a pet names array property to your CustomerPageModel:
public string[] PetNames {get;set;}
And turn the Pets property into a readonly calculated string:
public string Pets { get => string.Join(",", PetNames); }
And change the problem line in your LINQ expression to:
PetNames = ps.Select(x => x.Name).ToArray()
I changed (lamb to subquery)
string.Join(",", ps.Select(x => x.Name))
to
string.Join(",", (from y in PatientList where y.CustomerID == p.ID select y.Name).ToArray()),
I made the group later (after tolist)
var test = mylist.GroupBy(p => p.ID)
.Select(g => g.First())
.ToList();
problem solved
I'm trying to learn EF Core and hit this wall since I'm also fairly new to LINQ
Consider the model:
I'm trying to get all the distinct users from a single company;
The SQL statement would be something like this:
SELECT DISTINCT gau.AppUserId, au.Name, au.Id FROM Companies c
INNER JOIN Groups g ON g.CompanyId = c.Id
INNER JOIN GroupAppUsers gau ON gau.GroupId = g.Id
INNER JOIN AppUsers au ON gau.AppUserId = au.Id
Where c.Id = 40
Result:
How would I build this query like this? (Without the includes)
return await context.Companies
.Include(g => g.Groups)
.ThenInclude(au => au.AppUsers)
.ThenInclude(u => u.AppUser)
.SingleOrDefaultAsync(x => x.Id == id);
*Also, I'm not sure about the DB Model, I'm trying to avoid circular references but I think I should put Users linked with Companies instead of Groups, what do you think??
I'm trying to get all the distinct users from a single company
Rather than starting from companies and navigating to users, thus multiplying the users due to many-to-many relationship and then applying Disctinct operator, you could simply start from users and apply Any based criteria, thus eliminating the need of Disctinct at all.
Something like this (the DbSet / navigation property names could be different):
var companyUsers = await context.Users
.Where(u => u.UserGroups.Any(ug => ug.Group.Company.Id == id))
.ToListAsync();
Assuming your linking table (GroupAppUser) isn't modeled as an entity, something like:
var q = from c in db.Companies
from g in c.Groups
from u in g.AppUsers
select u;
or in Lambda form:
var q = db.Companies
.SelectMany(c => c.Groups)
.SelectMany(g => g.AppUsers);
Once you have the single Companies object, you can use the Navigation properties to get the AppUser objects:
return await context.Companies
.Include(g => g.Groups)
.ThenInclude(au => au.AppUsers)
.ThenInclude(u => u.AppUser)
.SingleOrDefaultAsync(x => x.Id == id)
.Groups.AppUsers.Distinct();
Is it a good practice or a convention to use dbContext within a Select linq query as following . If not what is the right convention or alternative to do so ?
dbContext.Employees.Select(x=>{
**Name = dbContext.ContactInformation.Where(y=>y.Id = x.Id),**
Id = x.Id
})
Why do not you have a navigationPropery from Employee to ContactInformation? look here
var result = dbContext.Employees.Include(e => e.ContactInformation);
You can also use a Join.
var res = dbContext.Employees.Join(ContactInformation,
e => e.Id,
c => c.Id,
(e, c) => new { e, c })
.Select(ec => ec.e);
SELECT DISTINCT k.* FROM [dbo].[kinds] K
INNER JOIN KindGraphic KG ON K.KindId = KG.KindId
INNER JOIN Graphics G ON KG.GraphicId = G.GraphicId
WHERE K.CategoryType = 2
AND G.IsSpecial = 1
How to write this in EF ? I am new to EF. I m using dbContex for my MVC project.
Make Note that "KindGraphic" table is mapped liked this ways
so I can not use this method https://stackoverflow.com/a/21986882/3264939
modelBuilder.Entity<Kind>()
.HasMany(c => c.Graphics)
.WithMany(g => g.Kinds)
.Map(t => t.MapLeftKey("KindId")
.MapRightKey("GraphicId")
.ToTable("KindGraphic"));
The result from your original query is some kind of complex result. So without selecting the exact columns (instead of using *), I assume the result is contained in an anonymous type like this:
{
Kind,
Graphic
}
I understand that KindGraphic is some kind of junction (join) table, so it's info is not important to include in the result (we can access KindId from Kind and GraphicId from Graphic). Here is the LINQ query:
var result = context.kinds.Where(e => e.CategoryType == 2)
.SelectMany(e=> e.Graphics.Where(g=>g.IsSpecial == 1),
(e, g) => new { Kind = e, Graphic = g} );
After your edit to use distinct, the query can be translated as you want all kinds having category type = 2 and any Graphics with IsSpecial = 1. So it should be like this:
var result = context.kinds.Where(e => e.CategoryType == 2 &&
e.Graphics.Any(g=>g.IsSpecial == 1));