I have a Flowable<Entity> entitiesand a Single<Set<Long>> attributeTypesToInclude. I would like to modify each entity - remove the attributes not present in attributeTypesToInclude and return the transformed Flowable<Entity>. If it weren't a single I could've just used a map over entities. I'm not sure how to achieve this with a Single involved.
Sample definitions of Entity and Attribute:
class Entity {
List<Attribute> attributes;
}
class Attribute {
long type;
String value;
}
I think flatMapSingle is what I was looking for. This could work:
entities
.flatMapSingle(entity -> transformEntitySingle(entity, attributesToInclude));
Single<Entity> transformEntitySingle(Entity entity, Single<List<Long>> attributesToInclude) {
return attributesToInclude
.map(attrs -> transformEntity(entity, attrs))
}
Entity transformEntity(Entity entity, List<Long> attributes) {
// Fairly trivial
}
Related
I'm using entity Framework 6.1, DbContext, Database First.
I know that I can get the DBsets by names like: context.Myobj1 , context.Myobj2.....
But Is there any possibility to do a for...each loop and to get one by one all the DbSet(of Tentity) on a DbContext?
You need to discover types of entities. That depends on your application. You can use reflection to discover those types. Or you can hardcode types of your entities.
After this you can loop though sets:
var types = new [] { typeof(User), typeof(Role) }; // just example
foreach(var type in types)
{
foreach(var entity in context.DbSet(type))
{ ... }
}
Is it possible to add summary properties(no database column) according LINQ from another property(column) in EF generated class from database and this property don't update(delete or remove from class) when update model from database(because this property(cloumn) is not on database)
Yes, it is. Classed generated by Entity Framework as an Entitied are always marked partial. It lets you extend the functionality with your own properties or method.
Let say your entity class is named Post. You can extend it with code like that:
public partial class Post
{
public int Average
{
get
{
return this.Items.Average();
}
}
}
Because it's not a part of designer-generated file it won't be overwritten when it's regenerated. However, there is one requirement to make it work: your custom part of Post class has to be in exactly the same namespace as code generated by EF.
Try using the [NotMapped] attribute on a property in a partial class. This will be ignored by Entity Framework.
public partial class EntityName
{
[NotMapped]
public int CalculatedProperty
{
get
{
return Numbers.Sum();
}
}
}
In this Virtual property that is used in an EF class why is it returning HashSet<T>? What is that class?
public virtual ICollection<TownShip> TownShips
{
get
{
return this.TownShips ?? (this.TownShips = new HashSet<TownShip>());
}
set
{
this.TownShips = value;
}
}
HashSet<T> is a generic class that implements the ICollection<T> interface. From the documentation:
The HashSet class provides high-performance set operations. A set
is a collection that contains no duplicate elements, and whose
elements are in no particular order.
In the code, if the property Townships is null, than an empty collection (HashSet) is returned.
HashSet of T's Documentation Here
I have a base class and two derived classes.
Each of the derived classes implements the same type as a property - the only difference is the property name.
Sadly I don't have much influence on the class design -> they have been generated from a wsdl file.
I then have a property on the BaseType to encapsulate the common property. The plan was to use this property in my web views etc.
I have used the famous "Fruit-Example" to demonstrate the problem:
public class FruitBase
{
public virtual int ID { get; set; }
//
// The plan is to use this property in mvc view
//
[NotMapped]
public virtual FruitnessFactor Fruitness
{
get
{
if (this.GetType().BaseType == typeof(Apple))
return ((Apple)this).AppleFruitness;
else if (this.GetType().BaseType == typeof(Orange))
return ((Orange)this).OrangeFruitness;
else
return null;
}
}
}
public class FruitnessFactor { }
In my MVC controller, the following query works absolutely fine:
return View(context.FruitEntities
.OfType<Apple>().Include(a =>a.AppleFruitness)
.ToList());
But this one doesn't:
return View(context.FruitEntities
.OfType<Apple>().Include(a =>a.AppleFruitness)
.OfType<Orange>().Include(o => o.OrangeFruitness)
.ToList());
The error message I get is:
DbOfTypeExpression requires an expression argument with a polymorphic result type that is compatible with the type argument.
I am using EF 5.0 RC and the Code First approach.
Any help is much appreciated!
As far as I can tell you can't apply Include on multiple subtypes in a single database query. You can query one type (OfType<Apple>().Include(a => a.AppelFruitness)) and the same for another subtype. The problem is that you can't concat the results in the same query because the result collections have different generic types (apples and oranges).
One option would be to run two queries and copy the result collection into a new collection of the base type - as you already indicated in the comment section under your question.
The other option (which would only need a single query) is a projection. You would have to define a projection type (you could also project into an anonymous type)...
public class FruitViewModel
{
public FruitBase Fruit { get; set; }
public FruitnessFactor Factor { get; set; }
}
...and then can use the query:
List<FruitViewModel> fruitViewModels = context.FruitEntities
.OfType<Apple>()
.Select(a => new FruitViewModel
{
Fruit = a,
Factor = a.AppleFruitness
})
.Concat(context.FruitEntities
.OfType<Orange>()
.Select(o => new FruitViewModel
{
Fruit = o,
Factor = o.OrangeFruitness
}))
.ToList();
If you don't disable change tracking (by using AsNoTracking) the navigation properties get populated automatically when the entities get attached to the context ("Relationship fixup") which means that you can extract the fruits from the viewModel collection...
IEnumerable<FruitBase> fruits = fruitViewModels.Select(fv => fv.Fruit);
...and you'll get the fruits including the FruitnessFactor properties.
This code is pretty awkward but a direct approach without using a projection has been asked for several times without success:
bottleneck using entity framework inheritance
Entity Framework - Eager loading of subclass related objects
How do I deeply eager load an entity with a reference to an instance of a persistent base type (Entity Framework 4)
I am trying to use a property on a POCO that uses LINQ to ENTITY to pull the first object out of a HashSet property on the same POCO. My object contains the following:
public virtual HashSet<ScheduleWaypoint> ScheduleWaypoints { get; set; }
public ScheduleWaypoint ArrivalStation {
get {
if (this.ScheduleWaypoints != null && this.ScheduleWaypoints.Count() > 0) {
return this.ScheduleWaypoints.Where(row => row.WaypointType.Type.Trim() == "SA").OrderByDescending(row => row.ScheduledTime).First();
} else
return null;
}
}
If I were working with just one object I can't say for certain if this would work but I know that it does not work inside other linq queries. I don't have access to the ID of the ScheduleWaypoint when creating the object, only after it is populated could I possibly do that. Is there a way that I can get this to work? Right now it is telling me:
The specified type member 'ArivalStation' is not supported in LINQ to
Entities. Only initializers, entity members, and entity navigation
properties are supported.
Is there something I can do to get access to this information on a property rather than constantly doing joins when I need the info?
Thanks.
You cannot use custom properties in linq-to-entities query. Only properties mapped directly to the database can be used = you must have sub query directly in your linq-to-entities query returning your ArrivalStation. Perhaps it can be wrapped as simple extension method:
public static IQueryable<ScheduleWaypoint> GetArrivalStation(this IQueryable<ScheduleWaypoints> waypoints, int routeId)
{
return waypoints.Where(w => w.WaypointType.Type.Trim() == "SA" && w.Route.Id == routeId)
.OrderByDescending(w => w.ScheduledTime)
.FirstOrDefault();
}
Where Route is your principal entity where way points are defined. FirstOrDefault is used because sub queries cannot use just First.