i have a legacy database (which is still used by another legacy application) where the group is denormalized and duplicated into the child rows
table parent
(
id
)
table child
(
id
parent_id
group_id
group_name
group_Flag
group_type
name
)
and i would like to map them to
class Parent
{
public long Id { get; private set; }
public ICollection<Group> Groups { get; private set; }
}
class Group
{
public long Id { get; set; }
public string Name { get; set; }
public GroupType Type { get; set; }
public bool Flag { get; set; }
public ICollection<Child> Childs { get; private set; }
}
class Child
{
public long Id { get; private set; }
public string Name { get; set; }
}
Is this possible?
How to do that in any of NHibernate's mapping methods (xml, MbC, Fluent, ...)
Update: Some additional info
the schema can't be changed because of the legacy application
additional views in the database are an option
leaking in the class model is possible
Here are some starters :
You could try to have a look at the "mapping collections" section of NHibernate reference :
- http://nhibernate.info/doc/nh/en/index.html#mapping-declaration-collections
Then, you could try to map the Groups property of Parent class using the "where" clause of the collection mapping :
(9) where (optional) specify an arbitrary SQL WHERE condition to be used when retrieving or removing the collection (useful if the collection should contain only a subset of the available data)
And map the Childs property of the Group class the same way.
Otherwise, you could create some views to present your data differently, and map your objects to those views (setting update="false" and insert="false" to your identifier property mapping)
Related
I was wondering why EF tries to add also foreign models.
Example:
public class Category
{
public int Id { get; set; }
public string Name{ get; set; }
}
public class Content
{
public int Id { get; set; }
public string Name{ get; set; }
public Category Category{ get; set; }
}
After creating "Content" using migrations, I have a table that includes the id of category. That's create. So I have three columns: Id, name and the categoryId. Seems EF "knows" that this should be just the primary key of Category, that needs to get stored.
Than I tried to add something with EF.
var cat = new Category {Id = 2, Name = "awesomeCat"})
var addContent = new Content({Name = "test", Category = cat})
Now I want to add a Content by using _context.Add(addContent). I was expecting a single insert into db that uses the name "test" and the categoryId 2. Id will be generated by DB.
But instead EF also tries to add a new Category into the category table.
So I took a deeper look and seems EF "does" not know it already exists and was not maintaining any transactions about the category model.
I gave it another try and used no new category, instead I was loading it before:
var cat = _context.findById("2");
and assigned this one instead. Now EF should know that this one already exists and does not have to add it in category table.
Could it be, that my model is just wrong.
Do I need to use it more like:
public class Content
{
public int Id { get; set; }
public string Name{ get; set; }
public int? CategoryId{ get; set; }
[ForeignKey("CategoryId")]
public Category Category{ get; set; }
}
Won't I get two category references then?
You need to tell EF Core it's a primary key and to generate the key
public class Category
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
}
public class Content
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
public Category Category { get; set; }
}
Then you don't need to mark [ForeignKey("CategoryId")], EF Core will turn the object reference into an ID in the database
If I misunderstood your question, ask again :)
EF Core has internal tracking of entities. When you simply new up a category, it's not being tracked. When you add the content, EF will track any related entities as well, which would include your category, which will by default be tracked as "Added". You have a few choices.
Don't "new up" an existing category, but rather, retrieve it from the database. If EF pulls it from the database, then it will be tracked, and will not be added again.
You can explicitly track the category instance you newed up and set it's state to "Unchanged".
_context.Attach(category);
_context.Entry(category).State = EntityState.Unchanged;
_context.Add(content);
The best method is to not deal with the reference property at all, and use an explicit foreign key property. Add a property to your content class:
public int CategoryId { get; set; }
Then, you can simply set this id, instead of the Category prop:
var addContent = new Content { Name = "test", CategoryId = 2 };
EF will backfill the reference property after save.
I have a constructed a model using code first in C#. The model literally represents a container element for a website building application, in other words, the model defines a Div tag or some such HTML element. Like a Div tag which can contain multiple child elements, I have tried to represent this in my model, but the scaffolding to the DB, does not give me what I'd expect.
I should get a new many to many joins table, but instead I only get a single column in the DB which expects a single int data type.
Here is the model:
public class ElementContainer
{
public int ElementContainerID { get; set; }
public int PageId { get; set; }
public int? ParentElementContainerID { get; set; }
public string ElementContainerName { get; set; }
public ElementType ElementType { get; set; }
public string ElementClass { get; set; }
public PageAsset PageAsset { get; set; } // content of container
public List<ElementContainer> NestedContainers { get; set; }
}
The last line is the self-referential attribute which just appears as a column called ElementContainer_ElementContainerID
Thanks in advance!
I agree with Bahman, DB first is easier.
While I haven't tried to do what you are trying, your code looks like a self-Join that would do exactly what you describe.
This is a One-to-Many relationship. EF Navigation will pull a List of all nested children containers.
If you want to create a many-to-many relationship with EF Code-First, you should create another Entity
public class ContainerChildren
{
public int ElementContainerID { get; set; }
public List<ElementContainer> NestedContainers { get; set; }
}
this reference should help you to get the exact idea http://blogs.msdn.com/b/wriju/archive/2011/05/14/code-first-ef-4-1-building-many-to-many-relationship.aspx
I have a class of Content which should be able to have a parentId for inheritance but also I want it to have a list of child content which is nothing to do with this inheritance tree.
I basically wanted a link table as ChildContentRelationship with Id's for parentContent and childContent in it and the Content class would have a list of ChildContentRelationship.
This has caused a lot of errors.
Here's waht I sort of want to do
public class Content
{
public int Id { get; set; }
public int? ParentContentId { get; set; }
public virtual Content ParentContent { get; set; }
public string Name { get; set; }
public int ContentTypeId { get; set; }
public virtual ContentType ContentType { get; set; }
public virtual ICollection<Property> Properties { get; set; }
public virtual ICollection<ChildContentRelationship> ChildContent { get; set; }
}
How would I set this up in EF?
I am not sure if I understand your model correctly. Let's discuss the options.
For a moment I omit this additional entity ChildContentRelationship and I assume the ChildContent collection is of type ICollection<Content>.
Option 1:
I assume that ParentContent is the inverse property of ChildContent. It would mean that if you have a Content with Id = x and this Content has a ChildContent with Id = y then the ChildContents ParentContentId must always be x. This would only be a single association and ParentContent and ChildContent are the endpoints of this same association.
The mapping for this relationship can be created either with data annotations ...
[InverseProperty("ParentContent")]
public virtual ICollection<Content> ChildContent { get; set; }
... or with Fluent API:
modelBuilder.Entity<Content>()
.HasOptional(c => c.ParentContent)
.WithMany(c => c.ChildContent)
.HasForeignKey(c => c.ParentContentId);
I think this is not what you want ("...has nothing to do with..."). Consider renaming your navigation properties though. If someone reads Parent... and Child... he will very likely assume they build a pair of navigation properties for the same relationship.
Option 2:
ParentContent is not the inverse property of ChildContent which would mean that you actually have two independent relationships and the second endpoint of both relationships is not exposed in your model class.
The mapping for ParentContent would look like this:
modelBuilder.Entity<Content>()
.HasOptional(c => c.ParentContent)
.WithMany()
.HasForeignKey(c => c.ParentContentId);
WithMany() without parameters indicates that the second endpoint is not a property in your model class, especially it is not ChildContent.
Now, the question remains: What kind of relationship does ChildContent belong to? Is it a one-to-many or is it a many-to-many relationship?
Option 2a
If a Content refers to other ChildContents and there can't be a second Content which would refer to the same ChildContents (the children of a Content are unique, so to speak) then you have a one-to-many relationship. (This is similar to a relationship between an order and order items: An order item can only belong to one specific order.)
The mapping for ChildContent would look like this:
modelBuilder.Entity<Content>()
.HasMany(c => c.ChildContent)
.WithOptional(); // or WithRequired()
You will have an additional foreign key column in the Content table in your database which belongs to this association but doesn't have a corresponding FK property in the entity class.
Option 2b
If many Contents can refer to the same ChildContents then you have a many-to-many relationship. (This is similar to a relationship between a user and roles: There can be many users within the same role and a user can have many roles.)
The mapping for ChildContent would look like this:
modelBuilder.Entity<Content>()
.HasMany(c => c.ChildContent)
.WithMany()
.Map(x =>
{
x.MapLeftKey("ParentId");
x.MapRightKey("ChildId");
x.ToTable("ChildContentRelationships");
});
This mapping will create a join table ChildContentRelationships in the database but you don't need a corresponding entity for this table.
Option 2c
Only in the case that the many-to-many relationship has more properties in addition to the two keys (ParentId and ChildId) (for example something like CreationDate or RelationshipType or...) you would have to introduce a new entity ChildContentRelationship into your model:
public class ChildContentRelationship
{
[Key, Column(Order = 0)]
public int ParentId { get; set; }
[Key, Column(Order = 1)]
public int ChildId { get; set; }
public Content Parent { get; set; }
public Content Child { get; set; }
public DateTime CreationDate { get; set; }
public string RelationshipType { get; set; }
}
Now your Content class would have a collection of ChildContentRelationships:
public virtual ICollection<ChildContentRelationship> ChildContent
{ get; set; }
And you have two one-to-many relationships:
modelBuilder.Entity<ChildContentRelationship>()
.HasRequired(ccr => ccr.Parent)
.WithMany(c => c.ChildContent)
.HasForeignKey(ccr => ccr.ParentId);
modelBuilder.Entity<ChildContentRelationship>()
.HasRequired(ccr => ccr.Child)
.WithMany()
.HasForeignKey(ccr => ccr.ChildId);
I believe that you want either option 2a or 2b, but I am not sure.
Suppose I have a table:
ID(pk) | HOME_EMAIL | WORK_EMAIL | OTHER_EMAIL
-------------------------------------------------
and the .NET classes
class A {
int id;
List<MyEmail> emails;
}
class MyEmail {
string email;
}
I suppose there's no way to map those (multiple) columns into a single collection in NHibernate, or is there? :)
It's come to a point that we'd rather not tinker with the database schema anymore so we can't do much with the database, if that helps.
I would suggest working with Interfaces so you could do something like this
interface IUser
{
int Id {get; set;}
IEnumerable<string> Emails {get;}
}
class MyUser : IUser
{
public int Id {get; set;}
public IEnumerable<string> Emails
{
get
{
return new [] { SomeEmail, SomeOtherEmail };
}
}
public string SomeEmail { get; set; }
public string SomeOtherEmail { get; set; }
}
Your application can expect an IUser and not care where we got the list of emails. You would map MyUser in NH, while the application does not (and should not) care about the actual implementation.
If it doesn't have to be a collection, but could be a custom type instead, say EmailAddresses which contains three properties:
public class EmailAddresses
{
public virtual string Home { get; set; }
public virtual string Work { get; set; }
public virtual string Other { get; set; }
}
You could use a component to map the three columns into the three properties of this object as a single property on the parent:
public class MyUser
{
...
public virtual EmailAddresses { get; set; }
}
You can map these in NHibernate using components or if you're using Fluent NHibernate with the ComponentMap<T> classmap (automapper can't do components).
There is a feature that's very close to what you want, <dynamic-component>
The documentation at http://nhibernate.info/doc/nh/en/index.html#components-dynamic should get you started.
I have a requirement to load a complex object called Node...well its not that complex...it looks like follows:-
A Node has a reference to EntityType which has a one to many with Property which in turn has a one to many with PorpertyListValue
public class Node
{
public virtual int Id
{
get;
set;
}
public virtual string Name
{
get;
set;
}
public virtual EntityType Etype
{
get;
set;
}
}
public class EntityType
{
public virtual int Id
{
get;
set;
}
public virtual string Name
{
get;
set;
}
public virtual IList<Property> Properties
{
get;
protected set;
}
public EntityType()
{
Properties = new List<Property>();
}
}
public class Property
{
public virtual int Id
{
get;
set;
}
public virtual string Name
{
get;
set;
}
public virtual EntityType EntityType
{
get;
set;
}
public virtual IList<PropertyListValue> ListValues
{
get;
protected set;
}
public virtual string DefaultValue
{
get;
set;
}
public Property()
{
ListValues = new List<PropertyListValue>();
}
}
public class PropertyListValue
{
public virtual int Id
{
get;
set;
}
public virtual Property Property
{
get;
set;
}
public virtual string Value
{
get;
set;
}
protected PropertyListValue()
{
}
}
What I a trying to do is load the Node object with all the child objects all at once. No Lazy load. The reason is I have thousands of Node objects in the database and I have to send them over the wire using WCF Service.I ran into the classes SQL N+ 1 problem. I am using Fluent Nhibernate with Automapping and NHibernate Profiler suggested me to use FetchMode.Eager to load the whole objects at once. I am using the following qyuery
Session.CreateCriteria(typeof (Node))
.SetFetchMode( "Etype", FetchMode.Join )
.SetFetchMode( "Etype.Properties", FetchMode.Join )
.SetFetchMode( "Etype.Properties.ListValues", FetchMode.Join )
OR using NHibernate LINQ
Session.Linq<NodeType>()
.Expand( "Etype")
.Expand( "Etype.Properties" )
.Expand( "Etype.Properties.ListValues" )
When I run any of the above query, they both generate one same single query with all the left outer joins, which is what I need. However, for some reason the return IList from the query is not being loaded property into the objects. Infact the returned Nodes count is equal to the number of rows of the query, so the Nodes objects are repeated.Moreover, the properties within each Node are repeated, and so do the Listvalues.
So I would like to know how to modify the above query to return all unique Nodes with the properties and list values within them.
each mapping has to have lazy loading off
in Node Map:
Map(x => x.EntityType).Not.LazyLoad();
in EnityType Map:
Map(x => x.Properties).Not.LazyLoad();
and so on...
Also, see NHibernate Eager loading multi-level child objects for one time eager loading
Added:
Additional info on Sql N+1:
http://nhprof.com/Learn/Alerts/SelectNPlusOne
I figure it out myself. The key is to use SetResultTransformer() passing an object of DistinctRootEntityResultTransformer as a parameter. So the query now looks like as follows
Session.CreateCriteria(typeof (Node))
.SetFetchMode( "Etype", FetchMode.Join )
.SetFetchMode( "Etype.Properties", FetchMode.Join )
.SetFetchMode( "Etype.Properties.ListValues", FetchMode.Join )
.SetResultTransformer(new DistinctRootEntityResultTransformer());
I found the answer to my questions through these links:
http://www.mailinglistarchive.com/html/nhusers#googlegroups.com/2010-05/msg00512.html
http://ayende.com/Blog/archive/2010/01/16/eagerly-loading-entity-associations-efficiently-with-nhibernate.aspx
I ended up with something like this:
HasMany(x => x.YourList).KeyColumn("ColumnName").Inverse().Not.LazyLoad().Fetch.Join()
Just make sure to select your entity like this, to avoid duplication due to the join:
session.CreateCriteria(typeof(T)).SetResultTransformer(Transformers.DistinctRootEntity).List<T>();
SetResultTransformer with DistinctRootEntityResultTransformer will only work for Main object but IList collections will be multiplied.