For the most part EF seems to handle itself quite well, using the following query in linq, I am able to get all the related table data using FK's without having to specify the one to many relationship.
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
from subpat in AP.DefaultIfEmpty()
orderby s.ClinicalAssetID descending
select new ClinicalASSPATVM
{
ClinicalAssetID = s.ClinicalAssetID,
ProductName = s.ProductName,
ModelName = s.ModelName,
SupplierName = s.SupplierName,
ManufacturerName = s.ManufacturerName,
SerialNo = s.SerialNo,
PurchaseDate = s.PurchaseDate,
PoNo = s.PoNo,
Costing = s.Costing,
TeamName = s.TeamName,
StaffName = s.StaffName,
InspectionDocumnets = subpat.InspectionDocumnets ?? String.Empty,
InspectionOutcomeResult = subpat.InspectionOutcomeResult
});
the above code pulls in the relationship data from the ViewModel.
public Product ProductName { get; set; }
public InspectionOutcome InspectionOutcomeResult { get; set; }
public Model ModelName { get; set; }
public BudgetCode Code { get; set; }
public AssetType AssetTypeName { get; set; }
public Manufacturer ManufacturerName { get; set; }
public Staff StaffName { get; set; }
public Team TeamName { get; set; }
public Supplier SupplierName { get; set; }
I have a new problem which I have created for myself. I wanted to add an ID Field to the Models entity this helps me filter the data in a drop down list. I called the Field Name: ModelAssetAsignmentID And when someone adds a new ModelName from the Clinical Controller the ModelAssetAsignmentID gets a value of two.
So when i added the Field ModelAssetAsignmentID to the model "Models" i created a second FK as such:
My Original Linq Query is now broken, it no longer displays the modelname. I'm guessing this is due to the two FK Constraints.
Making the following change did not work, the InnerException is null.
var ClinicalASSPATVM = (from s in db.ClinicalAssets
where (s.ModelAssetAssignmentID.Equals(2))
join cp in db.ClinicalPATs on s.ClinicalAssetID equals cp.ClinicalAssetID into AP
from subpat in AP.DefaultIfEmpty()
orderby s.ClinicalAssetID descending
The solution is to remove the second foreign key constraint ModelAssetAssignmentID and use a viewmodel to create a value in the ModelAssetAssignmentID, thus you then do not need to modify the linq query's.
Related
I am trying to learn LINQ query expressions. In MS website, I found this LINQ query.
public void Linq16()
{
List<Customer> customers = GetCustomerList();
var orders =
from c in customers
from o in c.Orders
where o.OrderDate >= new DateTime(1998, 1, 1)
select new { c.CustomerID, o.OrderID, o.OrderDate };
ObjectDumper.Write(orders);
}
I am not sure what that c.Orders does. I visualized customers and orders like data tables. Can someone tell me what this c.Orders does and what is it called?
It means that the entity Customer has a related entity, namely Order. The table might look like:
Order
OrderID
OrderData
CustomerID (this is a Foreign Key to the Customer table)
Customer
CustomerID
Name
...
The Entity Framework will recognize the relationship between the two tables and create classes, similar to following:
public class Customer
{
public int CustomerID { get; set; }
public virtual ICollection<Order> Orders { get; set; }
}
public class Order
{
public int OrderID { get; set; }
public DateTime OrderDate { get; set;}
public int CustomerID { get; set; }
public virtual Customer Customer { get; set; }
}
To understand the code a little more, the double from could be rewritten as:
foreach(Customer c in customers)
{
foreach(Order o in c.Orders)
{
if(o.OrderDate >= new DateTime(1998, 1, 1))
{
yield return new { c.CustomerID, o.OrderID, o.OrderDate };
}
}
}
This is NOT LINQ, but LINQ to entities.
Its a related entity. Basically its another table, and you can use it through including it.
When doing it with sql, you would have to select the table by the foreign key, EF does that automatically for you.
What you're doing there is the same as Include: MSDN blog example.
Include() is the Method syntax of the part of the query you dont understand.
Entity Framework creates a list of items of the other table as member of your entity - which is weird in the first place (just unusual actually) but very very useful, since you can ToList() the entity and they will be included if you .Include() them before.
To be very exact, you have a List (or something similar to list) added to the customer object (this is done by entity framework) and every Order is a line in the Orders table.
If you do want to use linq, but not Entity Framework, ignore it and search for other sources to learn linq.
Here is a really good resource to learn: MSDN, 101 LINQ examples
I have a typical many-to-many relationship with these 3 tables
[Post] (
[PostId] int, (PK)
[Content] nvarchar(max)
...
)
[Tag] (
[TagId] int, (PK)
[Name] nvarchar
...
)
[TagPost] (
[TagId] int, (PK, FK)
[PostId] int (PK, FK)
)
And, TagId and PostId are the PK and FK set on the tables accordingly etc. Then I have these classes and mapping in c#
public class Post {
public Post()
{
this.Tags = new HashSet<Tag>();
}
[Key]
public int PostId { get; set; }
...
public virtual ICollection<Tag> Tags { get; private set; }
}
public class Tag {
public Tag()
{
this.Posts = new HashSet<Post>();
}
[Key]
public int TagId { get; set; }
...
public virtual ICollection<Post> Posts { get; private set; }
}
internal class MyDbContext : DbContext
{
public DbSet<Post> Posts { get; set; }
public DbSet<Tag> Tags { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Post>().ToTable("Post");
modelBuilder.Entity<Tag>().ToTable("Tag");
modelBuilder.Entity<Post>()
.HasMany(x => x.Tags)
.WithMany(x => x.Posts)
.Map(x =>
{
x.ToTable("TagPost");
x.MapLeftKey("PostId");
x.MapRightKey("TagId");
});
}
Then I have this code to query them
var list = (from p in ctx.Posts.Include(p => p.Tags)
from t in p.Tags
where ... // some of my filter conditions
select p).ToList();
This join does return the posts I was looking for, however the returned posts don't their associated tags filled in even though I have the Include there. Could someone help point out what I'm missing so that I could have the tags also return with the posts?
Thanks a lot.
The double from is a manual Join which causes the Include to be ignored as mentioned here and here. Include is also ignored for other LINQ methods like grouping and projections.
Relationship fixup generally does not work for many-to-many relationships, only for relationships which have at least one single reference at one of the ends - one-to-many or one-to-one. If you project the Posts and related Tags into another type (anonymous or named) the data will be loaded correctly but because the relationship is many-to-many EF won't create the relationship in memory automatically so that the post.Tags collection will stay empty.
To get the Include working you must remove the second from from your query and apply the where clause directly to the Post entity parameter, for example like so:
var list = (from p in ctx.Posts.Include(p => p.Tags)
where p.Tags.Any(t => t.TagId == 1)
select p).ToList();
The filter by a Tag property is specified in the expression passed into .Any which is an expression with a Tag (t) as parameter.
try selecting everything into an anonymous object (something like this)
var list = (
from p in ctx.Posts
from t in p.Tags
where ... // some of my filter conditions
select new {
Posts = p,
Tags = p.Tags
})
.ToList();
Based on the feedback to my initial answer and the fact that EF can find the related entities but it is failing to populate the Tags collection I believe the issue lies in the definition of the Tags entity in the Post class.
Try removing the Hashset<> initialiser from the constructors and private from the set declaration:
public virtual ICollection<Tag> Tags { get; set; }
I am trying to create a ViewModel for data that I want to display in my view. The issue is, the data being displayed is spread across 2 databases and multiple tables within each. I've read that you cannot join Linq queries across multiple contexts, which makes sense, and I've also read that we can't use Code-First in EF5 to use Stored Procedures....which led me to using 3 different Linq queries and attempt to combine them into 1 ViewModel...I'm just not sure how to get there.
Here's my Linq queries:
var csdContext = new CSDContext(CustomerCode);
var masterContext = new MasterContext();
//Only returns 1 row - which is what we want.
List<Site> sites = (from s in csdContext.Sites
join sa in csdContext.SiteAddresses
on s.SiteID equals sa.SiteID
join a in csdContext.Addresses
on sa.AddressID equals a.AddressID
join spv in csdContext.SiteProductVersions
on s.SiteID equals spv.ProductVersionID
where s.SiteID == id
select s).ToList();
//List
List<States> states = (from s in masterContext.StatesTable
select s).ToList();
My ViewModel looks like this:
public class SiteDetailsViewModel
{
public string Address { get; set; }
public string Address2 { get; set; }
public string City { get; set; }
public string StateCode { get; set; }
public string ZipCode { get; set; }
public string OfficePhone { get; set; }
public string MobilePhone { get; set; }
public string AlternativePhone { get; set; }
public int ProductVersionID { get; set; }
}
Basically, I need the following data from these tables:
csdContext - Address
Address
Address2
City
ZipCode
csdContext - Sites
OfficePhone
MobilePhone
AlternativePhone
csdContext - SiteProductVersions
ProductVersionID
masterContext - States
StateCode
Here's how the tables are joined in SQL:
SELECT csd_a.Address, csd_a.Address2, csd_a.City, mstr_st.StateCode, csd_a.ZipCode, csd_s.OfficePhone, csd_s.MobilePhone,
csd_s.AlternativePhone, csd_spv.ProductVersionID
FROM CSD.dbo.Sites AS csd_s
INNER JOIN CSD.dbo.SiteAddress AS csd_sa ON csd_sa.SiteID = csd_s.SiteID
INNER JOIN CSD.dbo.Address AS csd_a ON csd_a.AddressID = csd_sa.AddressID
INNER JOIN CSD.dbo.SiteProductVersions AS csd_spv ON csd_s.SiteID = csd_spv.SiteID
INNER JOIN MasterDB.dbo.States AS mstr_st ON mstr_st.StateID = csd_a.StateID
I can't figure out how to merge these 3 results to create the ViewModel data for SiteDetailsViewModel. Can anyone help?
If you materialize your queries as described in OP you can use this:
var query = sites.Join(
states,
si => si.StateID,
st => st.StateID,
(si, st) => new SiteDetailsViewModel
{
Address = si.Address,
Address2 = si.Address2,
City = si.City,
StateCode = st.StateCode,
ZipCode = si.ZipCode,
OfficePhone = si.OfficePhone,
MobilePhone = si.MobilePhone,
AlternativePhone = si.AlternativePhone,
ProductVersionID = siProductVersionID
});
One possible alternate solution is to create views in DB #2 of the tables in DB #1. Then you can model/map those views in EF for DB #2. You would of course still need a context for DB #1 if you need to update any of the tables. But the benefit of this solution is that you can do all of your read access on a single context and get joins at the server instead of in memory.
So why don't you write it like this:
from ...
...
where s.SiteID == id
select new SiteDetailsViewModel()
{
Address = sa.Address,
Address2 = as.Address2,
..
}
Given the follow data class,
public class EmployeeMenu
{
public int ID { get; set; }
public string HeaderName { get; set; }
public List<string> ItemNames { get; set; }
}
how can I get a sub-query into the ItemNames field?
My current query of
IQueryable<EmployeeMenu> retValue =
from mh in menuHeaders
select new EmployeeMenu
{
ID = mh.ID,
HeaderName = mh.HeaderName,
ItemNames = (from mhi in mh.MenuItems
select mhi.MenuItemName).ToList<string>()
};
doesn't seem to be doing the trick...
The data structure is
MenuHeaders MenuItems
----------- ---------
ID ID
HeaderName <-(FK)--MenuHeaderID
MenuItemName
I ended up just changing from a List to IEnumerable. This fixed it.
Wouldnt you want to just put a where in your sub-select to filter that down to all the menu items with the MenuHeaderID equals mh.HeaderName. You can just .Equals() with the StringComparison type if you want as well.
Here is an example...
IQueryable<EmployeeMenu> retValue =
from mh in menuHeaders
select new EmployeeMenu
{
ID = mh.ID,
HeaderName = mh.HeaderName,
ItemNames = (from mhi in mh.MenuItems
select mhi.MenuItemName where mhi.MenuHeaderID = mh.HeaderName).ToList<string>()
};
My guess is that your not initiliazing the list within your class. I basing this off the experience I was having with Nhibernate.
public class EmployeeMenu
{
public int ID { get; set; }
public string HeaderName { get; set; }
public List<string> ItemNames { get; set; }
public EmployeeMenu()
{
ItemNames=new List<string>();
}
}
Hope this helps.
Okay. Try replacing
(from mhi in mh.MenuItems
select mhi.MenuItemName).ToList<string>()
by
mh.MenuItems
.AsEnumerable()
.Select(mhi => mhi.MenuItemName)
.ToList()
I question if you want a where clause in there somewhere, but this should get you past the runtime exception.
Any time you see an error message of the form "LINQ to Entities does recognize the method ... and this method can not be translated into a store expression" LINQ to Entities is telling you that it can't figure out how to translate part of the expression tree into a SQL statement. This means you need to pull things client side so that LINQ to Entities doesn't try to translate something that it can't translate.
The basic problem...
I have a method which executes the following code:
IList<Gig> gigs = GetGigs().WithArtist(artistId).ToList();
The GetGigs() method gets Gigs from my database via LinqToSql...
So, when GetGigs().WithArtist(artistId).ToList() is executed I get the following exception:
Member access 'ListenTo.Shared.DO.Artist Artist' of 'ListenTo.Shared.DO.Act' not legal on type 'System.Collections.Generic.List`1[ListenTo.Shared.DO.Act]
Note that the extension function "WithArtist" looks like this:
public static IQueryable<Gig> WithArtist(this IQueryable<Gig> qry, Guid artistId)
{
return from gig in qry
where gig.Acts.Any(act => (null != act.Artist) && (act.Artist.ID == artistId))
orderby gig.StartDate
select gig;
}
If I replace the GetGigs() method with a method that constructs a collection of gigs in code (rather than from the DB via LinqToSQL) I do NOT get the exception.
So I'm fairly sure the problem is with my LinqToSQl code rather than the object structure.
However, I have NO IDEA why the LinqToSQl version isnt working, so I've included all the associated code below. Any help would be VERY gratefully receivced!!
The LinqToSQL code....
public IQueryable<ListenTo.Shared.DO.Gig> GetGigs()
{
return from g in DBContext.Gigs
let acts = GetActs(g.ID)
join venue in DBContext.Venues on g.VenueID equals venue.ID
select new ListenTo.Shared.DO.Gig
{
ID = g.ID,
Name = g.Name,
Acts = new List<ListenTo.Shared.DO.Act>(acts),
Description = g.Description,
StartDate = g.Date,
EndDate = g.EndDate,
IsDeleted = g.IsDeleted,
Created = g.Created,
TicketPrice = g.TicketPrice,
Venue = new ListenTo.Shared.DO.Venue {
ID = venue.ID,
Name = venue.Name,
Address = venue.Address,
Telephone = venue.Telephone,
URL = venue.Website
}
};
}
IQueryable<ListenTo.Shared.DO.Act> GetActs()
{
return from a in DBContext.Acts
join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
from artist in art.DefaultIfEmpty()
select new ListenTo.Shared.DO.Act
{
ID = a.ID,
Name = a.Name,
Artist = artist == null ? null : new Shared.DO.Artist
{
ID = artist.ID,
Name = artist.Name
},
GigId = a.GigID
};
}
IQueryable<ListenTo.Shared.DO.Act> GetActs(Guid gigId)
{
return GetActs().WithGigID(gigId);
}
I have included the code for the Act, Artist and Gig objects below:
public class Gig : BaseDO
{
#region Accessors
public Venue Venue
{
get;
set;
}
public System.Nullable<DateTime> EndDate
{
get;
set;
}
public DateTime StartDate
{
get;
set;
}
public string Name
{
get;
set;
}
public string Description
{
get;
set;
}
public string TicketPrice
{
get;
set;
}
/// <summary>
/// The Act object does not exist outside the context of the Gig, therefore,
/// the full act object is loaded here.
/// </summary>
public IList<Act> Acts
{
get;
set;
}
#endregion
}
public class Act : BaseDO
{
public Guid GigId { get; set; }
public string Name { get; set; }
public Artist Artist { get; set; }
}
public class Artist : BaseDO
{
public string Name { get; set; }
public string Profile { get; set; }
public DateTime Formed { get; set; }
public Style Style { get; set; }
public Town Town { get; set; }
public string OfficalWebsiteURL { get; set; }
public string ProfileAddress { get; set; }
public string Email { get; set; }
public ImageMetaData ProfileImage { get; set; }
}
public class BaseDO: IDO
{
#region Properties
private Guid _id;
#endregion
#region IDO Members
public Guid ID
{
get
{
return this._id;
}
set
{
this._id = value;
}
}
}
}
I think the problem is the 'let' statement in GetGigs. Using 'let' means that you define a part of the final query separately from the main set to fetch. the problem is that 'let', if it's not a scalar, results in a nested query. Nested queries are not really Linq to sql's strongest point as they're executed deferred as well. In your query, you place the results of the nested query into the projection of the main set to return which is then further appended with linq operators.
When THAT happens, the nested query is buried deeper into the query which will be executed, and this leads to a situation where the nested query isn't in the outer projection of the query to execute and thus has to be merged into the SQL query ran onto the DB. This is not doable, as it's a nested query in a projection nested inside the main sql query and SQL doesn't have a concept like 'nested query in a projection', as you can't fetch a set of elements inside a projection in SQL, only scalars.
I had the same issue and what seemed to do the trick for me was separating out an inline static method call that returned IQueryable<> so that I stored this deferred query into a variable and referenced that.
I think this is a bug in Linq to SQL but at least there is a reasonable workaround. I haven't tested this out yet but my assumption is that this problem may arise only when referencing static methods of a different class within a query expression regardless of whether the return type of that function is IQueryable<>. So maybe it's the class that holds the method that is at the root of the problem. Like I said, I haven't been able to confirm this but it may be worth investigating.
UPDATE: Just in case the solution isn't clear I wanted to point it out in context of the example from the original post.
public IQueryable<ListenTo.Shared.DO.Gig> GetGigs()
{
var acts = GetActs(g.ID); // Don't worry this call is deferred
return from g in DBContext.Gigs
join venue in DBContext.Venues on g.VenueID equals venue.ID
select new ListenTo.Shared.DO.Gig
{
ID = g.ID,
Name = g.Name,
Acts = new List<ListenTo.Shared.DO.Act>(acts),
Description = g.Description,
StartDate = g.Date,
EndDate = g.EndDate,
IsDeleted = g.IsDeleted,
Created = g.Created,
TicketPrice = g.TicketPrice,
Venue = new ListenTo.Shared.DO.Venue {
ID = venue.ID,
Name = venue.Name,
Address = venue.Address,
Telephone = venue.Telephone,
URL = venue.Website
}
};
}
Note that while this should correct the issue at hand there also seems to be another issue in that the deferred acts query is being accessed in each element of the projection which I would guess would cause separate queries to be issued to the database per row in the outer projection.
I don't see anything in your classes to indicate how LINQ to SQL is meant to work out which column is which, etc.
Were you expecting the WithArtist method to be executed in .NET, or converted into SQL? If you expect it to be converted into SQL, you'll need to decorate your Gig class with appropriate LINQ to SQL attributes (or configure your data context some other way). If you want it to be executed in code, just change the first parameter type from IQueryable<Gig> to IEnumerable<Gig>.
I found out that an issue like this (which I also had recently) can be resolved, if you convert the IQueryable (or Table) variable Gigs into a list like so
return from g in DBContext.Gigs.ToList()
...
If that still doesn't work, do the same for all the IQueryables. The reason behind seems to me that some queries are too complex to be translated into SQL. But if you "materialize" it into a list, you can do every kind of query.
Be careful, you should add "filters" (where conditions) early because too much memory consumption can become a problem.