I have a sql statement that I want to be able to convert into EF4.
Its a simple Left outer join that looks like
SELECT *
FROM EntryDate
LEFT OUTER JOIN Member on Member.CardId = EntryDate.CardID
how do I do this using the entity framework 4?
If there is relation mapped in your model you can simply use navigation properties because they always use left join:
var data = members.EntryDates;
I expect you don't have such relation because CardId doesn't look like primary key of Member or EntryDate.
If you don't have navigation properties you must use
var query = from m in context.Members
join e in context.EntryDates on m.CardId equals e.CardId into x
from res in x.DefaultIfEmpty()
select new
{
Member = m,
EntryDate = res
};
This works only in EFv4+ because EFv1 didn't support DefaultIfEmpty.
Related
I need to process the query at the bottom of this post in C#. The query works, but I don't know how to use it in EF6. I used a method and a viewmodel for it (variable query = the query below). But when it encounters null values in the OUTER JOIN, int32 cant accept this value when calling .toList(). What's the best way to deal with it?
var result = context.Database.SqlQuery<TourQueryViewModel>(query);
var reslist = result.ToList();
I tried my first steps with LINQ, but I dont get it how to translate into LINQ itself or the query-methods, that are equivalent to it. So I am hoping for your help.
SELECT toursdata.TourId AS TourId, toursdata.Tourname AS Tourname,toursdata.Tourdate Tourdate,
toursdata.VehicleId AS VehicleId, toursdata.VehicleName AS VehicleName, toursdata.LicenseNumber AS LicenseNumber,
Employees.EmployeeId AS EmployeeId, Employees.Gender AS Gender, Employees.Forename AS Forename, Employees.Surname AS Surname
FROM (
SELECT te.TourId, te.Tourname, te.Tourdate,
Vehicles.VehicleId, Vehicles.VehicleName, Vehicles.LicenseNumber,
TourEmployees.EmployeeId
FROM TourEmployees RIGHT OUTER JOIN Tours AS te ON TourEmployees.TourId = te.TourId,
Tours AS tv INNER JOIN Vehicles ON tv.VehicleId = Vehicles.VehicleId
WHERE tv.TourId = te.TourId
) toursdata
LEFT OUTER JOIN Employees ON toursdata.EmployeeId = Employees.EmployeeId
To eliminate the null problem, I changed the data type of the corresponding entity-attribute to a nullable-type
int turned to int?.
Didnt know about that language feature.
I am having to convert code written by a former employee to work in a new database. In doing so I came across some joins I have never seen and do not fully understand how they work or if there is a need for them to be done in this fashion.
The joins look like this:
From Table A
Join(Table B
Join Table C
on B.Field1 = C.Field1)
On A.Field1 = B.Field1
Does this code function differently from something like this:
From Table A
Join Table B
On A.Field1 = B.Field1
Join Table C
On B.Field1 = C.Field1
If there is a difference please explain the purpose of the first set of code.
All of this is done in SQL Server 2012. Thanks in advance for any help you can provide.
I could create a temp table and then join that. But why use up the cycles\RAM on additional storage and indexes if I can just do it on the fly?
I ran across this scenario today in SSRS - a user wanted to see all the Individuals granted access through an AD group. The user was using a cursor and some temp tables to get the users out of AD and then joining the user to each SSRS object (Folders, reports, linked reports) associated with the AD group. I simplified the whole thing with Cross Apply and a sub query.
GroupMembers table
GroupName
UserID
UserName
AccountType
AccountTypeDesc
SSRSOjbects_Permissions table
Path
PathType
RoleName
RoleDesc
Name (AD group name)
The query needs to return each individual in an AD group associated with each report. Basically a Cartesian product of users to reports within a subset of data. The easiest way to do this looks like this:
select
G.GroupName, G.UserID, G.Name, G.AccountType, G.AccountTypeDesc,
[Path], PathType, RoleName, RoleDesc
from
GroupMembers G
cross apply
(select
[Path], PathType, RoleName, RoleDesc
from
SSRSOjbects_Permissions
where
Name = G.GroupName) S;
You could achieve this with a temp table and some outer joins, but why waste system resources?
I saw this kind of joins - it's MS Access style for handling multi-table joins. In MS Access you need to nest each subsequent join statement into its level brackets. So, for example this T-SQL join:
SELECT a.columna, b.columnb, c.columnc
FROM tablea AS a
LEFT JOIN tableb AS b ON a.id = b.id
LEFT JOIN tablec AS c ON a.id = c.id
you should convert to this:
SELECT a.columna, b.columnb, c.columnc
FROM ((tablea AS a) LEFT JOIN tableb AS b ON a.id = b.id) LEFT JOIN tablec AS c ON a.id = c.id
So, yes, I believe you are right in your assumption
I have this query
Select p.Name,p.Street from person p
left join address a on a.address_id = p.address_id
left join Order o on o.order_id = a.order_id
But when i try to convert it into LINQ query,
var q = from p in Entities.Person
from a in Entities.Address.Where(a=>a.address_id == p.address_id).DefaultIfEmpty()
from o in Entities.Order.Where (o=>o.order_id== a.order_Id).DefaultIfEmpty()
I am getting a Null exception since for some combination of address_ids there are no addresses and it blows up in o=>o.order_id== a.order_Id clause(since a is null).
Please let me know how to do multiple left joins in EF 4, the correct way !
Thanks !
If you have modeled correctly you do not need to explicitly do left outer joins.
Select p.Name, a.Street from person p
left join address a on a.address_id = p.address_id
left join Order o on o.order_id = a.order_id
The above query can be converted as follows
var projection = Entities.Person.Select(p => new {p.Name, p.Address.Street});
EF will automatically add the joins to retrieve the fields.
You can manually do the joins as follows
var projection = from p in Entities.Person
join a in Entities.Address on p.address_id equals a.address_id into outer
from a in outer.DefaultIfEmpty()
select new {p.Name, a.Street};
Lets say we have 3 tables, Users, Products, Purchases.
There is a view that needs to display the purchases made by a user.
I could lookup the data required by doing:
from p in DBSet<Purchases>.Include("User").Include("Product") select p;
However, I am concern that this may have a performance impact because it will retrieve the full objects.
Alternatively, I could select only the fields i need:
from p in DBSet<Purchases>.Include("User").Include("Product") select new SimplePurchaseInfo() { UserName = p.User.name, Userid = p.User.Id, ProductName = p.Product.Name ... etc };
So my question is:
Whats the best practice in doing this?
== EDIT
Thanks for all the replies.
[QUESTION 1]: I want to know whether all views should work with flat ViewModels with very specific data for that view, or should the ViewModels contain the entity objects.
Real example: User reviews Products
var query = from dr in productRepository.FindAllReviews()
where dr.User.UserId = 'userid'
select dr;
string sql = ((ObjectQuery)query).ToTraceString();
SELECT [Extent1].[ProductId] AS [ProductId],
[Extent1].[Comment] AS [Comment],
[Extent1].[CreatedTime] AS [CreatedTime],
[Extent1].[Id] AS [Id],
[Extent1].[Rating] AS [Rating],
[Extent1].[UserId] AS [UserId],
[Extent3].[CreatedTime] AS [CreatedTime1],
[Extent3].[CreatorId] AS [CreatorId],
[Extent3].[Description] AS [Description],
[Extent3].[Id] AS [Id1],
[Extent3].[Name] AS [Name],
[Extent3].[Price] AS [Price],
[Extent3].[Rating] AS [Rating1],
[Extent3].[ShopId] AS [ShopId],
[Extent3].[Thumbnail] AS [Thumbnail],
[Extent3].[Creator_UserId] AS [Creator_UserId],
[Extent4].[Comment] AS [Comment1],
[Extent4].[DateCreated] AS [DateCreated],
[Extent4].[DateLastActivity] AS [DateLastActivity],
[Extent4].[DateLastLogin] AS [DateLastLogin],
[Extent4].[DateLastPasswordChange] AS [DateLastPasswordChange],
[Extent4].[Email] AS [Email],
[Extent4].[Enabled] AS [Enabled],
[Extent4].[PasswordHash] AS [PasswordHash],
[Extent4].[PasswordSalt] AS [PasswordSalt],
[Extent4].[ScreenName] AS [ScreenName],
[Extent4].[Thumbnail] AS [Thumbnail1],
[Extent4].[UserId] AS [UserId1],
[Extent4].[UserName] AS [UserName]
FROM [ProductReviews] AS [Extent1]
INNER JOIN [Users] AS [Extent2] ON [Extent1].[UserId] = [Extent2].[UserId]
LEFT OUTER JOIN [Products] AS [Extent3] ON [Extent1].[ProductId] = [Extent3].[Id]
LEFT OUTER JOIN [Users] AS [Extent4] ON [Extent1].[UserId] = [Extent4].[UserId]
WHERE N'615005822' = [Extent2].[UserId]
or
from d in productRepository.FindAllProducts()
from dr in d.ProductReviews
where dr.User.UserId == 'userid'
orderby dr.CreatedTime
select new ProductReviewInfo()
{
product = new SimpleProductInfo() { Id = d.Id, Name = d.Name, Thumbnail = d.Thumbnail, Rating = d.Rating },
Rating = dr.Rating,
Comment = dr.Comment,
UserId = dr.UserId,
UserScreenName = dr.User.ScreenName,
UserThumbnail = dr.User.Thumbnail,
CreateTime = dr.CreatedTime
};
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
[Extent1].[Thumbnail] AS [Thumbnail],
[Extent1].[Rating] AS [Rating],
[Extent2].[Rating] AS [Rating1],
[Extent2].[Comment] AS [Comment],
[Extent2].[UserId] AS [UserId],
[Extent4].[ScreenName] AS [ScreenName],
[Extent4].[Thumbnail] AS [Thumbnail1],
[Extent2].[CreatedTime] AS [CreatedTime]
FROM [Products] AS [Extent1]
INNER JOIN [ProductReviews] AS [Extent2] ON [Extent1].[Id] = [Extent2].[ProductId]
INNER JOIN [Users] AS [Extent3] ON [Extent2].[UserId] = [Extent3].[UserId]
LEFT OUTER JOIN [Users] AS [Extent4] ON [Extent2].[UserId] = [Extent4].[UserId]
WHERE N'userid' = [Extent3].[UserId]
ORDER BY [Extent2].[CreatedTime] ASC
[QUESTION 2]: Whats with the ugly outer joins?
In general, only retrieve what you need, but keep in mind to retrieve enough information so your application is not too chatty, so if you can batch a bunch of things together, do so, otherwise you'll pay network traffic cost everytime you need to go back to the database and retrieve some more stuffs.
In this case, assuming you will only need those info, I would go with the second approach (if that's what you really need).
Eager loading with .Include doesn't really play nice when you want filtering (or ordering for that matter).
That first query is basically this:
select p.*, u.*, p2.*
from products p
left outer join users u on p.userid = u.userid
left outer join purchases p2 on p.productid = p2.productid
where u.userid == #p1
Is that really what you want?
There is a view that needs to display the purchases made by a user.
Well then why are you including "Product"?
Shouldn't it just be:
from p in DBSet<Purchases>.Include("User") select p;
Your second query will error. You must project to an entity on the model, or an anonymous type - not a random class/DTO.
To be honest, the easiest and most well performing option in your current scenario is to query on the FK itself:
var purchasesForUser = DBSet<Purchases>.Where(x => x.UserId == userId);
That should produce:
select p.*
from products p
where p.UserId == #p1
The above query of course requires you to include the foreign keys in the model.
If you don't have the FK's in your model, then you'll need more LINQ-Entities trickery in the form of anonymous type projection.
Overall, don't go out looking to optimize. Create queries which align with the scenario/business requirement, then optimize if necessary - or look for alternatives to LINQ-Entities, such as stored procedures, views or compiled queries.
Remember: premature optimization is the root of all evil.
*EDIT - In response to Question Update *
[QUESTION 1]: I want to know whether all views should work with flat ViewModels with very specific data for that view, or should the ViewModels contain the entity objects.
Yes - ViewModel's should only contain what is required for that View. Otherwise why have the ViewModel? You may as well bind straight to the EF model. So, setup the ViewModel which only the fields it needs for the view.
[QUESTION 2]: What's with the ugly outer joins?
That is default behaviour for .Include. .Include always produces a left outer join.
I think the second query will throw exception because you can't map result to unmapped .NET type in Linq-to-entities. You have to return annonymous type and map it to your object in Linq-to-objects or you have to use some advanced concepts for projections - QueryView (projections in ESQL) or DefiningQuery (custom SQL query mapped to new readonly entity).
Generally it is more about design of your entities. If you select single small entity it is not a big difference to load it all instead of projection. If you are selecting list of entities you should consider projections - expecially if tables contains columns like nvarchar(max) or varbinar(max) which are not needed in your result!
Both create almost the same query: select from one table, with two inner joins. The only thing that changes from a database perspective is the amount of fields returned, but that shouldn't really matter that much.
I think here DRY wins from a performance hit (if it even exists): so my call is go for the first option.
HI,
I have 3 tables: Clips, Books and relationships between ClipBook
Problem is:
i need get book that has bookID=4 with some clips i mean many-to-many
in simple text sql it will be something like this:
select * from Clips where clipID in (select clipID from ClipBook where bookID=4)
Question is:
How can i do this with Linq without operator Join of course
this could be a solution;
from cb in ClipBooks
where cb.BookID == 4
select cb.Clip;
or
ClipBooks.Where(cb => cb.BookId == 4).Select(cb => cb.Clip);
the Contains method is in Linq converted into the IN operator, example:
String[] cities = {"London", "Paris", "Madrid"};
from p in context.Person
where cities.Contains(p.Adress.City)
select p
is translated into a sql clause like: .. WHERE a.City in ('London', 'Paris', 'Madrid') where a is the Address table alias after the join with the Person table.
edit:
you could write a single query without a subquery, but this will be converted to a join most probably:
var clips = (from c in context.ClipBooks
where c.BookID == 4
select c.Clip).Distinct();
or
var clips = from c in context.Clip
where c.ClicBooks.Any( cb => cb.BookID == 4)
select c
Any is translated in Exists()