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));
Related
We are using EFCore.SqlServer.HierarchyId to represent a hierarchy in our data.
My goal is to return the descendants of an object with a particular path of indeterminate length, e.g. given a tree with the hierarchy one->two->three->four, the path one/two/three would return four
Knowing the length of the path, I can make a query like this:
var collections = await context.Collections.Where(c => c.CollectionHierarchyid.IsDescendantOf(
context.Collections.FirstOrDefault(c1 => c1.FriendlyId == "three" &&
context.Collections.Any(c2 => c2.CollectionHierarchyid == c1.CollectionHierarchyid.GetAncestor(1) && c2.FriendlyId == "two" &&
context.Collections.Any(c3 => c3.CollectionHierarchyid == c2.CollectionHierarchyid.GetAncestor(1) && c3.FriendlyId == "one")
)
).CollectionHierarchyid
)).ToListAsync();
But how would you go about this if the length of the path is unknown? I can't call a recursive function from the expression because it won't compile from Linq to Entity Sql.
I know the answer lies somewhere in using System.Linq.Expressions to build the expression, but I am not sure where to start.
The problem can be solved without dynamic expression tree generation, at least not directly, but using standard LINQ query operators.
Let say you have a hierarchical entity like this
public class Entity
{
public HierarchyId Id { get; set; }
// other properties...
}
Given a subquery returning the full set
IQueryable<Entity> fullSet = context.Set<Entity>();
and subquery defining some filtered subset containing the desired ancestors
IQueryable<Entity> ancestors = ...;
Now getting all direct and indirect descendants can easily be achieved with
IQueryable<Entity> descendants = fullSet
.Where(d => ancestors.Any(a => d.Id.IsDescendantOf(a.Id));
So the question is how to build ancestors subquery dynamically.
Applying some filter to the full set and retrieving the direct ancestors filtered by another criteria can be done by using simple join operator
from p in fullSet.Where(condition1)
join c in fullSet.Where(condition2)
on p.Id equals c.Id.GetAncestor(1)
select c
Hence all you need is to apply that recursively, e.g. having
IEnumerable<TArg> args = ...;
representing the filtering criteria arguments ordered by level, then the query can be built as follows
var ancestors = args
.Select(arg => fullSet.Where(e => Predicate(e, arg)))
.Aggregate((prevSet, nextSet) =>
from p in prevSet join c in nextSet on p.Id equals c.Id.GetAncestor(1) select c);
With that being said, applying it to your example:
IEnumerable<string> friendlyIds = new [] { "one", "two", "three" };
var fullSet = context.Collections.AsQueryable();
var ancestors = friendlyIds
.Select(friendlyId => fullSet.Where(e => e.FriendlyId == friendlyId))
.Aggregate((prevSet, nextSet) =>
from p in prevSet join c in nextSet on p.CollectionHierarchyid equals c.CollectionHierarchyid.GetAncestor(1) select c);
var descendants = fullSet
.Where(d => ancestors.Any(a => d.CollectionHierarchyid.IsDescendantOf(a.CollectionHierarchyid));
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();
I have a query with a left join in it:
var query = (from v in context.Vehicles
//left join vehicleAttributes
join va in context.VehicleAttributes on v.VehicleId equals va.VehicleId into vAttributes
from vehicleAttributes in vAttributes.DefaultIfEmpty()
where v.FleetId == fleetId
select new { v, vehicleAttributes });
And now I need to do a paging on it.
this works but gets all rows, so much more than i actually need
query.ToList().Select(x => x.v).Distinct().Skip(10 * (page - 1)).Take(10).ToList();
this is what I tried instead but now I don't have the joint values
query.Select(x => x.v).Distinct().ToList().Skip(10 * (page - 1)).Take(10).ToList();
any ideas?
Thanks
The ToList() triggers the call to the database so you need to only do this after you apply the Skip and Take. You'll need an OrderBy clause as well.
You should be able to do something like this:
var data = (from v in context.Vehicles
join va in context.VehicleAttributes on v.VehicleId equals va.VehicleId into vAttributes
from vehicleAttributes in vAttributes.DefaultIfEmpty()
where v.FleetId == fleetId
select new { v, vehicleAttributes })
.OrderBy(p => p.v.FleetId)
.Skip(10 * (page - 1))
.Take(10)
.ToList();
Don't call ToList before Skip. Doing so will return all the records in the database that match your query.
To use Skip on an EntityFramework query, you need to have an instance of IOrderedQueryable, so you need an OrderBy clause.
query
.Select(x => x.v)
.Distinct()
.OrderBy(v => v.FleetId)
.Skip(10 * (page - 1))
.Take(10).ToList();
I've got a project that takes care of a lot of this functionality. It's available on NuGet (with an MVC counterpart) and Google Code.
Using it would look something like this:
var factory = new Pagination.PageSourceFactory {
MaxItemsPerPage = 50,
DefaultItemsPerPage = 20
};
var source = factory.CreateSource(query, page);
I'm not sure how to get the rows I need in EF. In SQL it would look something like this:
SELECT * FROM [Recipes]
JOIN [UserFavorites] ON [UserFavorites].[RecipeId] = [Recipes].[Id]
WHERE [UserFavorites].[UserId] = #UserId
I know how to get the userfavorites that match the user id like this:
db.UserFavorites.Where(x => x.UserId == userId
But then how do I get all of the recipes that match the recipeIds inside of those userfavorites?
You can either use LINQ and construct a query:
var recipes = from r in db.Recipes
join f in db.UserFavorites on r.Id equals f.RecipeId
where f.UserId = userId
select r
or you can use the lambda syntax with navigation properties, assuming you have them set up for the relationships in question
var recipes = db.Recipes.Where(r => r.UserFavorites.Any(f => f.UserId == userId));
You can, of course, construct the actual query that's described in the first section using the equivalent lambda syntax (since the query syntax is just a language feature that compiles down to the equivalent calls to the extension methods using anonymous delegates), but that tends to be a little more difficult to read.
How about:
var recipes = context.Recipes
.SelectMany(r => r.Users, (r, u) => new { Recipe = r, User = u }
.Where(o => o.User.UserId = userId)
.Select(o => o.Recipe);
This implies UserFavorites is the intersection table between Recipes and Users
Recipes >- UserFavorites -< Users
I am using Entitry Framework 4.1 and I am struggling to understand how the convert the below query which uses joins and aggregate methods to a Linq to Entities call in the DomainService.
SELECT tblTime.Period As Timeline, COUNT(tblEngineeringDashboard_ItemList.ID) AS Items
FROM tblEngineeringDashboard_ItemList INNER JOIN
tblTime ON tblEngineeringDashboard_ItemList.TimeID = tblTime.ID
GROUP BY tblTime.Period
ORDER BY tblTime.Period
Can anyone provide help.
Possible Solution
Dim var = From i In ObjectContext.tblEngineeringDashboard_ItemList
Join t In ObjectContext.tblTimes On i.TimeID Equals t.ID
Group By i.TimeID Into Group
Select DateStart = (From n In ObjectContext.tblTimes Where n.ID = TimeID Select n.Period), PartCount = Group.Count
Phil
The first thing which comes to mind is:
var q = from t in Context.Time
group t by t.Period into g
orderby g.Key
select new
{
Timeline = g.Key,
Items = (from ti in g
from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
select il).Count()
};
However, the original SQL had an INNER JOIN, which would reject tblTime records without any matching records in tblEngineeringDashboard_ItemList. So you may want:
var q = from t in Context.Time
where t.ItemList.Any()
group t by t.Period into g
orderby g.Key
select new
{
Timeline = g.Key,
Items = (from ti in g
from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
select il).Count()
};
You can also flip the query around:
var q = from i in Context.EngineeringDashboardItemList
where i.Time != null
group i by i.Time.Period into g
orderby g.Key
select new
{
Timeline = g.Key,
Items = g.Count()
};
Does this work?
tblEngineeringDashboard_ItemList
.Join(tblTime,ed => ed.TimeID ,t => t.ID, (ed,t) => new{ed,t})
.GoupBy(g => g.t.Period)
.Select(s => new
{
Timeline = s.Key,
Items = s.Count()
}
)
.OrderBy(o => o.Timeline)
While converting from sql to linq isn't an ideal approach (you should think directly in linq, translating your need to a linq query), the query you posted is rather simple.
var grouped = tblTime.OrderBy(c => c.Period).GroupBy(c => c.Period).Select(c =>
new {
timeline = c.Key,
count = c.SelectMany(x => x.tblEngineeringDashboard).Count()
});
*Edit: There, fixed. Everything on the L2E engine.
This provided that there are correct foreign keys between the tables (thus you don't have to declare the join manually).