I have an entity that looks like this
public class SlideSet {
public SlideSet(string name) : this() {
Name = name
}
public SlideSet() {
Params = new HashSet<SlideSetParameter>();
}
[Required]
public string Name { get; set; }
public virtual ICollection<SlideSetParameter> Params { get; set; }
}
I just noticed that I'm not actually using the second constructor ever and that it actually makes no sense in my domain so I made it private. All of a sudden the Params array stopped loading and always gives me a length of 0. What's going on? In order for it to load I need my constructor to be at least protected. Why?
One of the conditions for EF to be able to create proxies (necessary for lazy loading) is
The class must have a public or protected parameter-less constructor.
From here (an old link, but this part still applies)
The proxy is a derived type and it must be able to call the parameterless constructor of the base type.
You need to have your default constructor set to public, as that is what Entity Framework is going to use to create your objects. Having it as private, it is unable to initialize the Params property, and therefor is trying to add any SlideSetParameters to a null object.
Related
I am consuming a REST Xml service.
I have all the necessary classes to do this, (supplied by the dev who wrote the service) but at my end I have to save some of the responses to the DB to perform the tasks of the app I am writing.
So I have marked some of these classes I need to put in the DB as partial and extended them so that I can inherit from a DbEntity class which specifies an ID property so I can use EF to save them to the DB thus:
public interface IDbEntity
{
int ID { get; set; }
}
[Serializable]
public class DbEntity : IDbEntity
{
[IgnoreDataMember]
[XmlIgnore]
public int ID { get; set; }
}
the problem I am facing now, is that when the service call is being de-serialized I get the error
Error in line 1 position 113. 'Element' 'ElementName' from namespace '' is not expected. Expecting element '_x003C_ID_x003E_k__BackingField'
I am simply making the call like this:
var response = await client.PostAsXmlAsync<TReq>("Some/API/Call", req);
TResp val = await msg.Content.ReadAsAsync<TResp>(response)
all the properties in the original classes have Orders specified with their DataMember attributes and I have clearly marked my DB properties to be Ignored, but to no avail.
is there any way I can get this to work? - ie getting the DataContractSerializer to actually ignore the properties I have marked to be ignored when de-serializing?
as an aside, these ignored properties are also being passed to the service when making a call - does IgnoreDataMember actually do anything?
seems that the way to do this is like this
public interface IDbEntity
{
int ID { get; set; }
}
[Serializable]
[DataContract]
public class DbEntity : IDbEntity
{
[XmlIgnore]
public int ID { get; set; }
}
so basically adding the DataContract Attribute but omitting the DataMember attribute on the item you don't want
don't know how I missed that first time around. seems its opt in rather than opt out in this instance.
Using Entity Framework 6.0, I am attempting to implement table splitting to improve query performance on tables with columns that contain BLOB data. I have followed the recommendations in this tutorial and it does indeed work as described.
Here's a very simplified example of the entity classes that map to one of my split tables ...
public class MyEntity
{
public string Id { get; set; }
public virtual MyEntityContent Content { get; set; }
public string Name { get; set; }
}
public class MyEntityContent
{
public string Id { get; set; }
public virtual MyEntity Entity { get; set; }
public byte[] Blob { get; set; }
}
... and the corresponding configuration code in the associated DbContext implementation ...
modelBuilder.Entity<MyEntity>().HasKey(e => e.Id).ToTable("MyEntities");
modelBuilder.Entity<MyEntityContent>().HasKey(c => c.Id).ToTable("MyEntities");
modelBuilder.Entity<MyEntity>().HasRequired(e => e.Content).WithRequiredPrincipal(d => d.Entity);
Given that the lazy-loaded Content property is Required by Entity Framework, it seems sensible to initialize it to a default value in the constructor of the containing MyEntity class ...
public MyEntity()
{
Content = new MyEntityContent();
}
... which enables a new instance of the class to be created and partially populated, without the risk of an exception being thrown by forgetting to initialize the required property value:
var entity = new MyEntity {Id = "XXX", Name = "something"};
I typically use a similar technique to initialize collection properties on EF entities and it works fine. However, in the above scenario, this initialization in the constructor has an unexpected effect: when retrieving existing entity instances from the database, the database value in the lazy-loaded property is ignored in favor of the empty default value.
This seems illogical to me. Doesn't Entity Framework create an entity object by first calling its default constructor and then applying its own property values to the created instance? If so, this should overwrite my default Content property value with a new instance of MyEntityContent, based on database data. This is how it seems to work with lazy-loaded collection properties.
If it's not possible to do this in the way I am expecting, is there an alternative technique for initializing lazy-loaded properties?
Don't initialize virtual members and perhaps, if you have to, handle any exceptions from uninitialized members.
I just had this issue with an entity with two virtual fields. Originally I had it initialize those two, but after removing them (and initializing the other fields to some default value), it started working for me. Try it out and let me know!
[Edit] I just realized I replied this to a slightly old post, didn't see the date. I guess I'll leave this answer here in case.
I haven't been able to find someone else with this issue specifically so here goes.
I have a simple model where one entity simply references another as a parent-child or one-to-many relationship defined like this:
public class Parent
{
public int ID { get; private set; }
public string Name { get; private set; }
}
public class Child
{
public int ID { get; private set; }
public string Name { get; private set; }
public virtual Parent Parent { get; private set; }
}
I am creating speicific mapping files for each, which work great for all the normal properties except for the related entity. It is always coming up null. No matter whether i have the virtual/private accessors on the property it will not load UNLESS i pull a copy of the parent separately from the context first. My mapping looks like this:
HasRequired(t => t.Parent).WithMany().Map(t => t.MapKey("ParentID")).WillCascadeOnDelete();
Is there anything I am doing wrong with this? I cannot for the life of me figure this out. Just so I cover all the bases, I am loading the entity like this:
Context.Set<Child>().FirstOrDefault(x => x.ID == 1);
And lastly here are some constraints I have:
I cannot have the foreign keys in my model as properties.
I cannot have a collection of children from the parent.
I finally figured it out. After much trial and error I noticed that having a parameterless constructor marked as internal, EF cannot create its dynamic proxy class of your type and therefore disables all lazy loading. I have two contructors, one for EF to hydrate objects, and another with parameters requires for callers to create my entity. Once I changed the signature to protected internal it started working. So I changed this:
internal Child() {}
to
protected internal Child() {}
May be you hasn't enable lazy loading .Try this,
Context.Set<Child>().FirstOrDefault(x => x.ID == 1).Include(c=>c.Parent);
I have the following Entity Models
public class User
{
public virtual long Id{get; set;}
[InverseProperty("Users")]
public virtual ICollection<Tag> Tags { get; protected set; }
}
public class Tag
{
public virtual long Id{get; set;}
internal protected virtual ICollection<User> Users { get; set; }
}
This is pure simple many-to-many relation User & Tag
I'm using Data Migrations. When I execute the command Add-Migration or Update-Database
I get the following error "The InversePropertyAttribute on property 'Tags' on type 'Kigg.DomainObjects.Entities.User' is not valid. The property 'Users' is not a valid navigation property on the related type 'Kigg.DomainObjects.Entities.Tag'. Ensure that the property exists and is a valid reference or collection navigation property."
When I changed the access modifier of Users property in Tag to public it worked fine and the generation is what I want.
From my design point of view I want to hide the Tag.Users property and make it protected or internal to keep it for internal use as I don't want to expose it to public API.
Note: I'm not discussing the my design here. I'm asking if it's possible to do that while Tag.Users is protected or internal?
I don't know how to make it work with data annotations but with Fluent API you can apply and experiment with the trick from here: http://blog.cincura.net/232731-mapping-private-protected-properties-in-entity-framework-4-x-code-first/
For your model it would look like the following:
public class User
{
public virtual long Id{get; set;}
public virtual ICollection<Tag> Tags { get; protected set; }
}
public class Tag
{
public virtual long Id{get; set;}
internal protected virtual ICollection<User> Users { get; set; }
public class PropertyAccessors
{
public static readonly Expression<Func<Tag, ICollection<User>>> Users
= t => t.Users;
}
}
Mapping in FluentAPI:
modelBuilder.Entity<User>()
.HasMany(u => u.Tags)
.WithMany(Tag.PropertyAccessors.Users);
This works and creates the expected many-to-many relationship.
But I am not sure if you can do anything useful with that navigation property. The fact that you have the property protected and virtual lets me guess that you basically want lazy loading support inside of the entity class or derived classes.
The problem is that apparently (according to my tests at least) lazy loading doesn't work for anything else than a public property. The loaded tag is a proxy but the navigation collection is always null (unless the property is public).
Moreover, even eager and explicit loading don't work:
Outside of the Tag class:
// Eager loading
var tag = context.Tags.Include(Tag.PropertyAccessors.Users).First();
// Explicit loading
var tag2 = context.Tags.First();
context.Entry(tag2).Collection(Tag.PropertyAccessors.Users).Load();
Or inside of the Tag class (some method in Tag which gets the context passed):
public DoSomething(MyContext context)
{
// Eager loading
var tag = context.Tags.Include(t => t.Users).First();
// Explicit loading
context.Entry(this).Collection(t => t.Users).Load();
}
In all cases I get an exception that the property Users on entity Tag is not a valid navigation property. (The exception disappears as soon as I make the property public.)
I don't know if adding/removing/updating relationships would work. (I doubt.)
It looks that you can map a non-public navigation property with this approach to generate the expected database schema. But it seems that there is nothing useful you can do with it.
I don't know much about EF5 but you can use the attribute InternalsVisibleToAttribute to make internal members visible to a specific assembly.
It looks like that MEF framework creates objects which have default CTOR. How about customized CTOR, or Constructor with parameters? For example:
[Export (typeof(IInterface1))]
public class MyClass : IInterface1
{
public MyClass(int id) {....}
....
}
If not, one way I can think is to pass object as parameters to CTOR. For example:
public Interface IParameterID {
public int Id { get; private set; }
...
}
Then the CTOR will be:
public MyClass([Import(typeof(IParameter))] IParameterID id)
{ ... }
Not sure if it is possible to add attribute to CTOR's parameters? And the next question is that if MEF will automatically create an instance of IParameter and inject it to the CTOR's parameter?
Yes, this is possible. Just put an [ImportingConstructorAttribute] on the constructor you would like to use. The parameters will automatically be treated as imports, but if you need to change the contract name on them you can also put an import attribute on them.