I have an entity called Requirements and an entity called Actions and an entity called Requirement_Fulfillment that is a composite of the Requirement and Action primary keys but also has an integer field.
To better illustrate, Requirement has a navigation property Requirement_Fulfillmments, Action also has a navigation property Requirement_Fulfillments, and Requirement_Fulfillment has 2 navigation properties for Requirement and Action.
If I want to add a Requirement_Fulfillment, and I specify the primary key so that it matches up with Requirement's and Action' primary key will it automatically be added to their navigation properties?
Or do I need to manually add it to the navigation properties of both sides or one side?
The navigation properties are just that, a link to the other entity. You wouldn't add to the navigation property, you would add to the entity itself and then access it via a navigation property.
Related
Im trying to generate a model from a database. The model is being generated but all the foreign key fields (that should be only navigation properties) are being mapped as Navigation Property and a scalar property (IN THE MODEL).
I know the foreign key is added in the end of the multiplicity on database but whenever I generate a database from model, all the entity classes doesn't contain that field.
Is there a way to ignore this field generating the model from database?
When you generate the model from the database there is a check box called Include foreign key columns in the model. This check box is by default selected. If you deselect it your model will not contain foreign key properties but just navigation properties.
I am new to Entity Framework. When the Visual Studio creates Model diagram we can see mainly two things in Entities.Propertie and Navigation Properties,So what are these Navigation Properties? How to use them?
Navigation properties represents related entites to the principal entity. Foreign Keys are usually represented by navigation properties.
Ex : if you have two tables Invoice and invoice items and those tables have a relation 1-> many so you'll find a navigation property in invoice entity that lists all invoice items related to an invoice.
Hope it helps.
Navigation properties in the Entity Framework provide a way to navigate an association between two entity types. Every object can have a navigation property for every relationship in which it participates. Navigation properties allow you to navigate and manage relationships in both directions, returning either an EntityReference, if the multiplicity is either one or zero-or-one, or an EntityCollection, if the multiplicity is many.
When you use the Entity Framework-generated classes, navigation properties are created for objects that participate in a relationship.
UPDATE: Here is nice navigation properties example for relations between books, authors and publishers.
Navigation Property is mainly used for Foreign key relationship in EF. i.e. User to Roles, product to categories etc.
so if you have Order with OrderLines, navigation property will say Order_OrderLineItems and you can access complete line items associated with it.
have a look some of the explanation here, What are Navigation Properties in Entity Framework for?
I would like to have entity which can have a child (one or zero). This child is same type as parent. I am not sure how to set entity framework becouse I would like to have two navigation properties for every entity. One for navigation to child and one for navigation to parent. Basically it is exactly the same structure as doubly linked list.
I think this table structure should be enough:
int | id | PK
int | id_next | FK
text | data
But how can I create navigation properties for next/prev items? I am able to create only navigation property for next item.
Thanks for help.
You can't. The problem here is that a one-to-one relation has a very specific requirement - FK value must be unique in the whole table. Once the uniqueness is not enforced you can add a second entity pointing to the same parent and you have a one-to-many relation.
To enforce this in a self referencing relation like you described in your example you will place an unique index on the id_next and it will work in SQL server. The problem is that entity framework doesn't support unique keys. Because of that entity framework is only able to build one-to-one relations between two different entity types where FK in the dependent the entity type is also its PK (the only way how to force FK to be unique) = both entities has same PK value. This cannot work with a self referencing relation because you cannot have two same PK values in one table.
You can do this in EF4 by specifying a 0..1 -> 0..1 relationship on the entity. Name one of the navigation properties "Previous" and the other "Next". This will create a hidden field on the underlying DB.
I haven't thoroughly tested this approach but it seemed to work when I created the database script.
Research Tree structures in the Entity Framework. You basically want a vertical tree (i.e. one branch). The framework won't enforce only one branch, but you can manage that in your business logic.
I don't want to use foreign key association to CompanyType (member that will hold the foreign key id) but prefer to use navigation property. So I removed the CompanyTypeId.
I get this exception that relates the relationship between entity Company and CompanyType:
Error 5: The element 'Principal' in
namespace
'http://schemas.microsoft.com/ado/2008/09/edm'
has incomplete content. List of
possible elements expected:
'PropertyRef' in namespace
'http://schemas.microsoft.com/ado/2008/09/edm'.
How can I remove those id's from the POCOs without getting the exception?
This is the difference between Foreign key association and Independent association. Both associations use navigation properties but only Foreign key association uses FK property as well. You can either remove them globally as #Robbie mentioned or you can change the type manually for selected relation.
Select the relation in entity framework designer
In properties remove Referential constraints
Go to Mapping window and map the relation
Here is the screen shot from one of my testing application with one-to-many relation between Order and OrderLine entities:
As you can see there is no OrderId in the OrderLine entity and referential constraints of the relation are empty. Also mapping of the relation is specified.
BUT you can't never remove Id from CompanyType. Ids (PKs) are mandatory. You can only change its accessibility in its properties.
When you imported in your Model from your DB you are asked if you want to:
"Include Foreign key columns in the model"
you need to switch this off.
I generated an Entity Framework Model (4.0) from my database. I did not design the database and do not have any control over the schema, but there are a few tables that do not have foreign key constraints defined, but there is an implicit relationship defined.
For example:
I have a table called People that has the following columns:
GenderID
RaceID
There are tables for both Gender and Race but there is no foreign key in the People table.
When I imported the model it did not add Navigation Properties for these relationships. I tried to add it manually but From Role and To Role are disabled. I'm not sure how to add the relationship myself. How do I do this?
Yup - it's not that straightforward.
Here's what you do:
1 - Right click on the designer, Add -> Association
2 - Setup the association and cardinalities (People *..1 Gender, People *..1 Race)
3 - Go into the Model Browser -> Associations
4 - Right click on your newly created associations, click Properties
5 - Here you need to setup the endpoints for the key and cascade options. Make sure you get the endpoints correct. You can also setup a referential constraint here for your implicit navigational property.
6 - Map the navigational property to the relevant tables/fields.
7 - Validate your model, cross your fingers.
I came across this blog post which proposes the following solution, which worked great for me (unfortunately I could not get RPM1984's to work in my situation).
Add an Association via designer background right click contextual menu
Set up your Association (be sure to uncheck creation of foreign key)
Right click on the association and choose Properties
Click on the ... button for Referential Constraint
Set up the relation between the keys within
Verify (from the designer contextual menu)
???
Profit!