I have quite a number of DbSets hanging off of my DbContext. The generic type for each of these DbSets derives from a common base class.
How can I query a common property in the base class across all of the DbSets?
To illustrate, say for instance I have the following two DbSets:
public DbSet<Person> People { get; set; }
public DbSet<Vehicle> Vehicles { get; set; }
Both Person and Vehicle derive from EntityBase.
public class Person : EntityBase {
...
}
public class Vehicle : EntityBase {
...
}
Say EntityBase is defined as follows:
public class EntityBase {
public virtual string ExampleProperty { get; set; }
}
How can I select the values of ExampleProperty across all of the DbSets? For my contrieved example I could do a simple union, but I am looking for an easy way to query across all DbSets holding types deriving from EntityBase, since I have hundreds of them.
I can query the change tracker as follows, but that will only work for entities with pending changes.
dbContext.ChangeTracker
.Entries<EntityBase>()
.Select(obj => obj.Entity)
.Select(obj => obj.ExampleProperty);
How can I do the same thing for all entities?
I was able to grab the data I need using the following query (I prefer the fluent API):
dbContext.GetType().GetProperties()
.Where(p => p.PropertyType.IsGenericType)
.Where(p => p.PropertyType.GetGenericTypeDefinition() == typeof(DbSet<>))
.Where(p => p.PropertyType.GetGenericArguments().First().IsSubclassOf(typeof(EntityBase)))
.SelectMany(p => (IEnumerable<EntityBase>)p.GetValue(dbContext, null))
.Select(obj => obj.ExampleProperty);
Unfortunately, the SQL generated is querying all columns for each of the DBSet types which is pulling quite a bit of data into memory.
Related
I want to use class inheritance for filtering rows in database which is not absolutery normal and relational. There is table entities mapped to model Entity via EF Core:
[Table("entities")]
public class Entity
{
public int Id { get; set; }
public string Type { get; set; }
}
Type is some string that can be "A" or "B" e.g.
I want to specify class EntityA : Entity for entities with type A and accordingly for B:
public class EntityA : Entity
{
// some unique A properties
}
public class EntityB : Entity
{
// some unique B properties
}
Basically my DBContext looks like
public class ApplicationContext : DbContext
{
public DbSet<Entity> Entities { get; set; }
// ...
}
Can I defined EntitiesA and EntitiesB in my DBContext using filtering by Type?
I wanted to write it at least in stupid way:
public List<EntityA> EntitiesA
{
get
{
return Entity.Where(x => x.Type == "A").ToList();
}
}
But there is class casting problem (because code returns List, not List) and also it's not like ORM-style solution, EntitiesA is not DBSet, load query automatically and so on.
Okay, I found, It's called Discriminator in EF Core, those who interested can read here: https://learn.microsoft.com/en-us/ef/core/modeling/inheritance
I don't think it's a good idea to bring EntitiesA and EntitiesB to DBContext. Because basically, it contains some of the application domain knowledge (Business Layer), which should be completely decoupled with your DBContext (Data Access Layer).
I suggest to have a EntityLoader in Business Layer which is responsible for loading Entities from DB and return list of EntityA or B.
Regarding the class casting problem, you can fix the compile error with
return Entity.Where(x => x.Type == "A").Select(x => (EntityA)x).ToList();
However, you will get a runtime error since the Entity type is less specific than the EntityA type. Which mean you need to convert like this
return Entity.Where(x => x.Type == "A").Select(x => new EntityA(....)).ToList();
I'm currently attempting to use Entity Framework's ChangeTracker for auditing purposes. I'm overriding the SaveChanges() method in my DbContext and creating logs for entities that have been added, modified, or deleted. Here is the code for that FWIW:
public override int SaveChanges()
{
var validStates = new EntityState[] { EntityState.Added, EntityState.Modified, EntityState.Deleted };
var entities = ChangeTracker.Entries().Where(x => x.Entity is BaseEntity && validStates.Contains(x.State));
var entriesToAudit = new Dictionary<object, EntityState>();
foreach (var entity in entities)
{
entriesToAudit.Add(entity.Entity, entity.State);
}
//Save entries first so the IDs of new records will be populated
var result = base.SaveChanges();
createAuditLogs(entriesToAudit, entityRelationshipsToAudit, changeUserId);
return result;
}
This works great for "normal" entities. For simple many-to-many relationships, however, I had to extend this implementation to include "Independent Associations" as described in this fantastic SO answer which accesses changes via the ObjectContext like so:
private static IEnumerable<EntityRelationship> GetRelationships(this DbContext context, EntityState relationshipState, Func<ObjectStateEntry, int, object> getValue)
{
context.ChangeTracker.DetectChanges();
var objectContext = ((IObjectContextAdapter)context).ObjectContext;
return objectContext
.ObjectStateManager
.GetObjectStateEntries(relationshipState)
.Where(e => e.IsRelationship)
.Select(
e => new EntityRelationship(
e.EntitySet.Name,
objectContext.GetObjectByKey((EntityKey)getValue(e, 0)),
objectContext.GetObjectByKey((EntityKey)getValue(e, 1))));
}
Once implemented, this also worked great, but only for many-to-many relationships that use a junction table. By this, I'm referring to a situation where the relationship is not represented by a class/entity, but only a database table with two columns - one for each foreign key.
There are certain many-to-many relationships in my data model, however, where the relationship has "behavior" (properties). In this example, ProgramGroup is the many-to-many relationship which has a Pin property:
public class Program
{
public int ProgramId { get; set; }
public List<ProgramGroup> ProgramGroups { get; set; }
}
public class Group
{
public int GroupId { get; set; }
public IList<ProgramGroup> ProgramGroups { get; set; }
}
public class ProgramGroup
{
public int ProgramGroupId { get; set; }
public int ProgramId { get; set; }
public int GroupId { get; set; }
public string Pin { get; set; }
}
In this situation, I'm not seeing a change to a ProgramGroup (eg. if the Pin is changed) in either the "normal" DbContext ChangeTracker, nor the ObjectContext relationship method. As I step through the code, though, I can see that the change is in the ObjectContext's StateEntries, but it's entry has IsRelationship=false which, of course, fails the .Where(e => e.IsRelationship) condition.
My question is why is a many-to-many relationship with behavior not appearing in the normal DbContext ChangeTracker since it's represented by an actual class/entity and why is it not marked as a relationship in the ObjectContext StateEntries? Also, what is the best practice for accessing these type of changes?
Thanks in advance.
EDIT:
In response to #FrancescCastells's comment that perhaps not explicitly defining a configuration for the ProgramGroup is cause of the problem, I added the following configuration:
public class ProgramGroupConfiguration : EntityTypeConfiguration<ProgramGroup>
{
public ProgramGroupConfiguration()
{
ToTable("ProgramGroups");
HasKey(p => p.ProgramGroupId);
Property(p => p.ProgramGroupId).IsRequired();
Property(p => p.ProgramId).IsRequired();
Property(p => p.GroupId).IsRequired();
Property(p => p.Pin).HasMaxLength(50).IsRequired();
}
And here are my other configurations:
public class ProgramConfiguration : EntityTypeConfiguration<Program>
{
public ProgramConfiguration()
{
ToTable("Programs");
HasKey(p => p.ProgramId);
Property(p => p.ProgramId).IsRequired();
HasMany(p => p.ProgramGroups).WithRequired(p => p.Program).HasForeignKey(p => p.ProgramId);
}
}
public class GroupConfiguration : EntityTypeConfiguration<Group>
{
public GroupConfiguration()
{
ToTable("Groups");
HasKey(p => p.GroupId);
Property(p => p.GroupId).IsRequired();
HasMany(p => p.ProgramGroups).WithRequired(p => p.Group).HasForeignKey(p => p.GroupId);
}
When these are implemented, EF still does not show the modified ProgramGroup in the ChangeTracker.
While the concept of "relationship with attributes" is mentioned in the theory of entity-relationship modelling, as far as Entity Framework is concerned, your ProgramGroup class is an entity. You're probably unwittingly filtering it out with the x.Entity is BaseEntity check in the first code snippet.
I believe the problem lies in the definition of your Program and Group class and overridden SaveChanges method. With the current definition of the classes the EF is unable to use change tracking proxies, that catch changes as they are being made. Instead of that the EF relies on the snapshot change detection, that is done as part of SaveChanges method. Since you call base.SaveChanges() at the end of the overridden method, the changes are not detected yet when you request them from ChangeTracker.
You have two options - you can either call ChangeTracker.DetectChanges(); at the beginning of the SaveChanges method or change definition of your classes to support change tracking proxies.
public class Program {
public int ProgramId { get; set; }
public virtual ICollection<ProgramGroup> ProgramGroups { get; set; }
}
public class Group {
public int GroupId { get; set; }
public virtual ICollection<ProgramGroup> ProgramGroups { get; set; }
}
The basic requirements for creating change tracking proxies are:
A class must be declared as public
A class must not be sealed
A class must not be abstract
A class must have a public or protected constructor that does not have parameters.
A navigation property that represents the "many" end of a relationship must have public virtual get and set accessors
A navigation property that represents the "many" end of a relationship must be defined as ICollection<T>
Entity Framework represents many-to-many relationships by not having entityset for the joining table in CSDL, instead it manages this through mapping.
Note: Entity framework supports many-to-many relationship only when the joining table does NOT include any columns other than PKs of both the tables
you should have to define navigation property yourself to coupe with this proplem.
this link can be of your help.
Assume I have the following entity classes:
public class Customer {
public int Id { get; set; }
public virtual ICollection<Order> Orders { get; set; }
}
public class Order {
public int Id { get; set; }
public virtual Customer Customer { get; set; }
}
How should those be mapped in Entity Framework 6 fluent code-first mapping? I want to be explicit about the mapping and not rely on automatic mapping conventions.
Option 1
Just map the local properties of both classes. That's how I would do it in Fluent NHibernate.
public class CustomerMap : EntityTypeConfiguration<Customer> {
public CustomerMap() {
HasMany(x => x.Orders);
}
}
public class OrderMap : EntityTypeConfiguration<Order> {
public OrderMap() {
HasRequired(x => x.Customer);
}
}
Option 2
Map both sides of the relationship in both classes.
public class CustomerMap : EntityTypeConfiguration<Customer> {
public CustomerMap() {
HasMany(x => x.Orders).WithRequired(x => x.Customer);
}
}
public class OrderMap : EntityTypeConfiguration<Order> {
public OrderMap() {
HasRequired(x => x.Customer).WithMany(x => x.Orders);
}
}
Option 3
Map both sides of the relation, but only in one of the classes. The code would be similar to option 2, just one of the two constructors would be empty.
Is there any difference between those options? If yes, please also explain why I should or shouldn't use a specific option.
I would go for option 3.
In option 1 you can forget to map the inverse end of an association. In this simple example it's clear that Order.Customer and Customer.Orders are two ends of the same association. When things get more complex, this isn't always obvious. Also, it is redundant code.
In option 2 you could have conflicting mappings. For instance when you have...
HasOptional(x => x.Customer).WithMany(x => x.Orders);
...in OrderMap, you will get a runtime exception telling you that both mappings don't match. And again, it is redundant code.
So option 3 is DRY and safe. The only issue is that it's a bit arbitrary where to configure the mappings. I tend to adhere to mapping children in their parent's mapping.
One more comment. You may want to add a primitive property CustomerId in Order. The mapping would look like:
public class CustomerMap : EntityTypeConfiguration<Customer>
{
public CustomerMap()
{
HasMany(x => x.Orders).WithRequired(x => x.Customer)
.HasForeignKey(o => o.CustomerId);
}
}
Now you have full control over both ends of the association and the foreign key name to be used. Besides that, there are some advantages of these foreign key associations as opposed to independent associations (without a primitive foreign key property). For instance, the ability to establish an association without having to fetch the parent object from the database. You can just by set an Id value.
I'm trying to implement a TPC inheritance model in EF 4.3 CodeFirst for an existing Oracle database (over which I have no control). I have several sub-types that each map to its own table. Unfortunately, some of the key columns are of datatype number(18,0) instead of integer. EF seems to hate me now.
Here's my base class:
public abstract class Vehicle
{
public virtual int Id { get; set;}
public virtual string Color { get; set; }
//more properties
}
Here are some example sub-types:
public class Car : Vehicle
{
//more properties
}
public class Truck : Vehicle
{
//more properties
}
public class Motorcycle : Vehicle
{
//more properties
}
And here's my DbContet:
public class VehicleDataContext : DbContext
{
public DbSet<Vehicle> Vehicles { get; set; }
public DbSet<Car> Cars { get; set; }
public DbSet<Truck> Trucks { get; set; }
public DbSet<Motorcycle> Motorcycles { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Vehicle>().HasKey(x => x.Id);
modelBuilder.Entity<Car>().Map(m => m.MapInheritedProperties());
modelBuilder.Entity<Car>().Property(x => x.Id).HasColumnType("decimal");
modelBuilder.Entity<Truck>().Map(m => m.MapInheritedProperties());
modelBuilder.Entity<Truck>().Property(x => x.Id).HasColumnType("int");
modelBuilder.Entity<Motorcycle>().Map(m => m.MapInheritedProperties());
modelBuilder.Entity<Motorcycle>().Property(x => x.Id).HasColumnType("decimal");
base.OnModelCreating(modelBuilder);
}
}
So, I already know to MapInheritedProperties so that all the properties of the base and sub-type are mapped to one table. I'm assuming that I have to tell the base that it HasKey so that EF doesn't complain that my DbSet<Vehicle> doesn't have a key mapped. I'd like to be able to assume that I can "tell" each entity how to map its own key's column type like I've done above. But I think that's not quite it.
Here's a test that fails:
[TestFixture]
public class when_retrieving_all_vehicles
{
[Test]
public void it_should_return_a_list_of_vehicles_regardless_of_type()
{
var dc = new VehicleDataContext();
var vehicles = dc.Vehicles.ToList(); //throws exception here
Assert.Greater(vehicles.Count, 0);
}
}
The exception thrown is:
The conceptual side property 'Id' has already been mapped to a storage
property with type 'decimal'. If the conceptual side property is
mapped to multiple properties in the storage model, make sure that all
the properties in the storage model have the same type.
As mentioned above, I have no control over the database and it's types. It's silly that the key types are mixed, but "it is what it is".
How can I get around this?
You cannot achieve it through mapping. This is limitation of EF code first. You can map each property (including the key) in inheritance structure only once. Because of that you can have it either integer or decimal in all entities in the inheritance tree but you cannot mix it.
Btw. what happens if you try to use int or decimal for the whole inheritance tree? Does it fail for loading or persisting entity? If not you can simply use the one (probably decimal if it can use whole its range) for all entities.
Say I have the following class with an aggregation of an external class:
public class MyMovie
{
public virtual string id{get;set;}
public virtual Movie movie{get;set;}
}
//These classes are externally defined and cannot be changed.
public class Movie
{
public string title{get;set;}
public IList<Director> Directors{get;set;}
}
public class Director
{
public string name{get;set;}
public IList<Movie> DirectedMovies{get;set;}
}
The db schema for this would be three tables:
Movie(m_id, title)
Director(d_id, name)
Directs(m_id, d_id)
Is it possible to map this with fluent nhibernate? I just don't understand how this would be done with the many to many relation being in the external classes where I cannot map create a map class for Director as this does not define members as virtual.
Map your class MyMovie as usual, and use disable lazyloading of Movie and Director. Aftter all lazy-loading for many-to-many part should work as usualy, cause for collection laziness proxy is not need.
public class MyMovieMap : ClassMap<MyMovie>
{
public MyMovieMap()
{
Id(x => x.id);
References(x => x.movie);
}
}
public class MovieMap : ClassMap<Movie>
{
public MovieMap()
{
Not.LazyLoad();
Id<int>("m_id");
Map(x => x.title);
HasManyToMany(x => x.Directors)
.Table("Directs")
.LazyLoad();
}
}
public class DirectorMap : ClassMap<Director>
{
public DirectorMap()
{
Not.LazyLoad();
Id<int>("d_id");
Map(x => x.name);
HasManyToMany(x => x.DirectedMovies)
.Table("Directs")
.LazyLoad();
}
}
Basically, your issue here is that you are trying to tell nhibernate to load objects, but it doesn't know anything about the objects. For instance, you are telling it MyMovie contains a Movie, yet it doesn't know what field Movie.title belongs to, and it doesn't know how to join in Director's with the movies because it is unmapped. So basically in order to pull this off without a mapping file, you need to use Criteria and result transformers to accomplish this (basically issuing a sql query and converting the results to objects via an on the fly mapping), you could encapsulate this logic in a function so it can be called in your code without being too messy, but other than that I can't see any other way around it. Check out this post, the code is not exactly what you are trying to do (because you will have to join in directors), but it is using the same tools you will have to use... http://ayende.com/blog/2741/partial-object-queries-with-nhibernate