I am using complicated SQL queries, i have to use SqlQuery ... in simple way:
MODEL:
public class C
{
public int ID { get; set; }
[NotMapped]
public float Value { get; set; }
}
CONTROLLER:
IEnumerable<C> results = db.C.SqlQuery(#"SELECT ID, ATAN(-45.01) as Value from C);
return View(results.ToList());
VIEW:
#model IEnumerable<C>
#foreach (var item in Model) {
#Html.DisplayFor(modelItem => item.Value)
}
and the result for item.Value is NULL.
So my question is , how can i print the computed value from SQL Query ?
Thank you for help.
I would conclude from the fact that Value is 0 that EF doesn't map returned columns to properties that are not mapped in the model.
What you could try as an alternative is to define a helper type...
public class CHelper
{
public int ID { get; set; }
public float Value { get; set; }
}
Then query into this type and copy the values to your entity afterwards:
IEnumerable<C> results = db.Database.SqlQuery<CHelper>(
#"SELECT ID, ATAN(-45.01) as Value from C")
.Select(ch => new C
{
ID = ch.ID,
Value = ch.Value
});
(Normally in a LINQ-to-Entities query you cannot project into an entity with Select. But I believe that the Select in the example above does not affect the database query and is LINQ-to-Objects in memory, so it should be allowed. I am not sure, though.)
Note that the results collection is not attached to and tracked by the context, but I guess you don't need it anyway for a GET request to render a view.
Of course you could create your view directly based on the CHelper class as view model and omit the conversion into the C entity.
Related
I am teaching myself asp .net mvc3. I have researched a lot but the more I read the more confused I become. I want to create a page where users can register their property for sale or rent.
I have created a database which looks like this:
public class Property
{
public int PropertyId { get; set; }
public int PropertyType { get; set; }
ยทยทยท
public int Furnished { get; set; }
...
}
Now, I want dropdownlistfor = PropertyType and Furnished.
Property type would be
1 Flat
2 House
3 Detached House
...
Furnished would be:
1 Furnished
2 UnFurnished
3 PartFurnished
...
Now, I am really not sure where to keep this information in my code. Should I have 2 tables in my database which store this lookup? Or should I have 1 table which has all lookups? Or should I just keep this information in the model?
How will the model bind to PropertyType and Furnished in the Property entity?
Thanks!
By storing property types and furnished types in the database, you could enforce data integrity with a foreign key, rather than just storing an integer id, so I would definitely recommend this.
It also means it is future proofed for if you want to add new types. I know the values don't change often/will never change but if you wanted to add bungalow/maisonette in the future you don't have to rebuild and deploy your project, you can simply add a new row in the database.
In terms of how this would work, I'd recommend using a ViewModel that gets passed to the view, rather than passing the database model directly. That way you separate your database model from the view, and the view only sees what it needs to. It also means your drop down lists etc are strongly typed and are directly in your view model rather than just thrown into the ViewBag. Your view model could look like:
public class PropertyViewModel
{
public int PropertyId { get; set; }
public int PropertyType { get; set; }
public IEnumerable<SelectListItem> PropertyTypes { get; set; }
public int Furnished { get; set; }
public IEnumerable<SelectListItem> FurnishedTypes { get; set; }
}
So then your controller action would look like:
public class PropertiesController : Controller
{
[HttpGet]
public ViewResult Edit(int id)
{
Property property = db.Properties.Single(p => p.Id == id);
PropertyViewModel viewModel = new PropertyViewModel
{
PropertyId = property.Id,
PropertyType = property.PropertyType,
PropertyTypes = from p in db.PropertyTypes
orderby p.TypeName
select new SelectListItem
{
Text = p.TypeName,
Value = g.PropertyTypeId.ToString()
}
Furnished = property.Furnished,
FurnishedTypes = from p in db.FurnishedTypes
orderby p.TypeName
select new SelectListItem
{
Text = p.TypeName,
Value = g.FurnishedTypeId.ToString()
}
};
return View();
}
[HttpGet]
public ViewResult Edit(int id, PropertyViewModel propertyViewModel)
{
if(ModelState.IsValid)
{
// TODO: Store stuff in the database here
}
// TODO: Repopulate the view model drop lists here e.g.:
propertyViewModel.FurnishedTypes = from p in db.FurnishedTypes
orderby p.TypeName
select new SelectListItem
{
Text = p.TypeName,
Value = g.FurnishedTypeId.ToString()
};
return View(propertyViewModel);
}
}
And your view would have things like:
#Html.LabelFor(m => m.PropertyType)
#Html.DropDownListFor(m => m.PropertyType, Model.PropertyTypes)
I usually handle this sort of situation by using an enumeration in code:
public enum PropertyType {
Flat = 1,
House = 2,
Detached House = 3
}
Then in your view:
<select>
#foreach(var val in Enum.GetNames(typeof(PropertyType)){
<option>val</option>
}
</select>
You can set the id of the option equal to the value of each item in the enum, and pass it to the controller.
EDIT: To directly answer your questions:
You can store them as lookups in the db, but for small unlikely to change things, I usually just use an enum, and save a round trip.
Also look at this approach, as it looks better than mine:
Converting HTML.EditorFor into a drop down (html.dropdownfor?)
How can I return return a collection in a method from a LINQ query that has a one to many relationship?
For instance, I have the following code where I can have many Projects to a TimeTracking object. Will the type that I have defined for the return type (IEnumerable) work? It is set up in my EF model as this specific kind of relationship.
public IEnumerable<TimeTracking> GetTimeTrackings()
{
YeagerTechEntities DbContext = new YeagerTechEntities();
DbContext.Configuration.ProxyCreationEnabled = false;
DbContext.Configuration.LazyLoadingEnabled = false;
var timeTrackings = (from timeTrackingProjects in DbContext.TimeTrackings.Include("TimeTrackings.Projects")
select timeTrackingProjects).Where(p => p.TimeTrackingID > 0);
CloseConnection(DbContext);
return timeTrackings;
}
If so, when I display it in my MVC 3 View, and my View contains an IEnumerable<YeagerTech.YeagerTechWcfService.TimeTracking> model, will the model variable have records in it for the TimeTracking and Project objects? I don't think it will. My TimeTracking object is set up as follows unless I need to inherit the Project class with it (which would then have the Project properties):
public partial class TimeTracking
{
[DataMember]
public int TimeTrackingID { get; set; }
[DataMember]
public short ProjectID { get; set; }
[DataMember]
public byte[] Attachment { get; set; }
[Required]
[DataType(DataType.Date)]
[DataMember]
public System.DateTime StartDate { get; set; }
[Required]
[DataType(DataType.Date)]
[DataMember]
public System.DateTime EndDate { get; set; }
[DataMember]
public string Notes { get; set; }
[DataMember]
public System.DateTime CreatedDate { get; set; }
[DataMember]
public Nullable<System.DateTime> UpdatedDate { get; set; }
[DataMember]
public virtual Project Project { get; set; }
}
I also want my View to display the Project text that is associated with the TimeTracking and not the Project value. How can I do this?Can someone please help?
I got the following msg from invoking a method on my WCF client.
'cannot be serialized if reference tracking is disabled'
After getting the msg, I then modified my DataContracts to include references ([DataContract(IsReference = true)]).
namespace YeagerTechModel
{
[Serializable]
[DataContract(IsReference = true)]
public partial class Customer
{
public Customer()
{
this.Projects = new HashSet<Project>();
}
[DataMember]
public short CustomerID { get; set; }
[Required]
[StringLength(50)]
[DataType(DataType.EmailAddress)]
[DataMember]
public string Email { get; set; }
I am executing the following server side code to successfully get data from my database in a parent/child relationship. The Include method explicity invokes getting the related Project data for the specific Customer. I had to do it this way because you must turn LazyLoading off if you want to get your parent/child data across the wire.
If I look at the WCF messagelog, I can see the actual data coming across in a Customer object and it has the Project object inside of the Customer object.
However, after the call is made and I actually inspect the contents of the "customer" variable, I don't see any refernces to any Project data.
public IEnumerable<Customer> GetCustomers()
{
YeagerTechEntities DbContext = new YeagerTechEntities();
DbContext.Configuration.ProxyCreationEnabled = false;
DbContext.Configuration.LazyLoadingEnabled = false;
IQueryable<Customer> customer = DbContext.Customers.Include("Projects").Where(p => p.CustomerID > 0);
CloseConnection(DbContext);
return customer;
}
The thing I want to do now, is reference the Project data coming back from the call. However, I don't get any Customer object intellisense after typing "customer.". It's all pertains to an IQueryable object.
I'm passing it back into my MVC Controller as the following type:
IEnumerable<YeagerTechWcfService.Customer> customerList = db.GetCustomers();
and into my View as the following model:
IEnumerable<YeagerTech.YeagerTechWcfService.Customer>
Now, the big question is "How can I reference the Project data coming back in my View?
The below is my code for the View, but there is no intellisense for "item.Project". Note that "Email" is a property inside my Customer object.
foreach (var item in Model)
{
<tr>
<td>
#Html.DisplayFor(modelItem => item.Email)
</td>
Looks like your Linq query should be closer to this (NOTE: did not test the query, might need tweaking):
var query = (from tt in DbContext.TimeTrackings.Include("Projects")
where tt.TimeTrackingID > 0
select tt).ToList();
Linq query as you have written is deferred execution, you are closing your connection before retrieving the data, so that would probably cause a runtime error.
.Include() statement should specify the property on the entity (TimeTracking in your case) that need to be loaded, so in this case that would be Project property
Once you have retrieved your enumerable collection of TimeTracking entities you can access the properties of the Project entity associated with a particular TimeTracking entity like so:
foreach(var tracking in GetTimeTrackings())
{
foreach(var project in tracking.Projects)
{
// Assuming your Project entity has a Name property
Response.Write(project.Name);
}
}
I'm not sure what you mean by
I also want my View to display the Project text that is associated
with the TimeTracking and not the Project value.
can you clarify what property from which entity you want to see? What is the Project Entity definition?
In response to your comment about closing connection after retrieving the data:
The statement IQueryable<Customer> customer = DbContext.Customers.Include("Projects").Where(p => p.CustomerID > 0); does not actually execute a query against the database until you start to iterate it (most likely in your view with a foreach statement). If you add a .ToList() at the end of that statement, it will execute it and return a List<Customer> (which is also IEnumerable) which contains all the records that are result of your query.
When you try to type customer. to get intellisense for the Customer entity, you're not seeing it because customer is a list of Customer entities (or rather an IQueryiable of them) so you would need to do something like customer[0]. to access the properties of the first Customer entity in that list (or iterate over it).
I'm not 100% sure how entity references come through in ASP.NET MVC on a model entity but a really simple way you can get this done is create a model class you want to use in your view, say something like this:
public class TimeTrackingModel {
public int TimeTrackingID { get; set; }
public string ProjectName { get; set; }
}
then in your query do this:
var customers = (from tt in DbContext.TimeTrackings.Include("Projects")
where tt.TimeTrackingID > 0
select new TimeTrackingModel { TimeTrackingID = tt.TimeTrackingID, ProjectName = tt.Project.ProjectName }).ToList();
then in your view specify IEnumberable<TimeTrackingModel> as the model and then access the properties like this:
foreach (var item in Model)
{
<tr>
<td>
#Html.DisplayFor(modelItem => item.ProjectName)
</td>
Actually, after further review, I can now see the Project collection in my Customer collection all the way back up to my client after adding a QucikWatch on the object.
The correct answer is the last part of my post where the LazyLoadingEnabled = false appears.
I am using ASP.NET MVC 3 with Entity Framework 4 using POCOs and want to query a set and select some properties to put into my viewModel. I will sketch a simplified version of my situation:
Situation:
I have an entity BananaTree containing a collection of Banana
public class Banana
{
public int Id { get; set; }
public int Size { get; set; }
public TimeSpan Age { get; set }
public string Description { get; set; }
}
public class BananaTree
{
public int Id { get; set; }
public ICollection<Banana> Bananas { get; set; }
}
I also have a view model BananaListItemViewModel used in the view showing a list of bananas for a certain banana tree. This view is managed by the BananaTreeController
public class BananaListItemViewModel
{
public int Id { get; set; }
public TimeSpan Age { get; set }
}
I have a Details action on the controller like so:
public ActionResult Details(int bananaTreeId)
{
var viewModel = from bananaTree in bananaTreeRepository.BananaTrees
where bananaTree.Id == bananaTreeId
from banana in bananaTree.Bananas
select new BananaListItemViewModel
{
Id = banana.Id,
Age = banana.Age
};
return View(viewModel);
}
What I want to change
This works fine and now I only select the items from the database that I need for my view model. However, I want to take out some more logic from my controller and am trying to do this as much as possible.
I would like to have a function in my repository like so:
IQueryable<Banana> GetBananas(int bananaTreeId)
{
return (from bananaTree in BananaTrees
where bananaTree.Id == bananaTreeId
select bananaTree.Bananas).Single().AsQueryable();
}
and use it like so:
public ActionResult Details(int bananaTreeId)
{
var viewModel = from banana in bananaTreeRepository.GetBananas(bananaTreeId)
select new BananaListItemViewModel
{
Id = banana.Id,
Age = banana.Age
};
return View(viewModel);
}
Question
My question is, in this case, will the two queries be combined and go to the database in one go like in my first example or will this first get all the bananas from the tree completely out of the database and perform the second query on that list? I would prefer the first case. If not, could I rewrite the GetBananas query to get that behaviour (for example like the query below)?
IQueryable<Banana> GetBananas(int bananaTreeId)
{
return from bananaTree in BananaTrees
where bananaTree.Id == bananaTreeId
from banana in bananaTree.Bananas
select banana;
}
Thanks very much in advance.
In your specific case, it will be only one query, if the call to Single() doesn't lead to the query to be executed. Unfortunately, I couldn't find any info on whether it does or does not. The call to AsQueryable does not trigger the execution as long, as the Bananas property really is an IQueryable.
According to http://msdn.microsoft.com/en-us/library/bb156472.aspx, the call to Single doesn't execute your query.
Conclusion:
You code should result in only one query.
In general:
You can pass an IQueryable from one method to another without it being implicitly executed.
The following code will result in only one SQL statement executed at the end, when the call to ToList happens:
IQueryable<Banana> GetBananasByWeight(int weight)
{
return from banana in Bananas where banana.Weight = weight;
}
IQueryable<Banana> FilterByQuality(IQueryable<Banana> bananaQuery, int quality)
{
return bananaQuery.Where(b => b.Quality == quality);
}
public List<Banana> GetBananas(int weight, int quality)
{
var query = GetBananasByWeight(weight);
var filteredBananas = FilterByQuality(query, quality);
return filteredBananas.ToList();
}
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.