I have a entity and a many to many table associate with it. Because the many2many table have a nchar field, it can not be mapped to a association in EFv1. Is that possible to create a Entity hold both the original entity and the nchar field? Thanks!
You can map such a table, but not as a many to many association with properties, because associations in the EF don't have properties. Instead, you'll have two entities with one to many associations to a third entity representing the association.
Related
Are there ways to make one-to-many (abstract) relation without using SQL foreign keys?
I know it could be made by joining 2 non-related tables. But is it possible to use EF Core default navigation tools?
I think you want that because you can't add a foreign-key to your entity
So, you can solve that so:
You have a entity
Group
and you want a
List<User>
but your User can't be assigned to one group.
So you create a
GroupUser
entity which has a foreign key for the
List<GroupUser>
and a navigation property to the User
This is called a many-to-many relationship
I am using Spring data JPA(Hibernate).
I am trying to join my tables (Table A & Table B) but on Non-Primary Columns. Is it possible to actually do that? I am trying to use referenceColumnName, but it seems to not working, giving error :
Cannot set int to Integer.
When I am removing referenceColumnName, then it is working but obviously it is joining with Primary Key. Also in case of One-to-one Bidirectional, where should I place mappedBy & JoinColumn?
The annotation #JoinColumn indicates that this entity is the owner of the relationship (that is: the corresponding table has a column with a foreign key to the referenced table), whereas the attribute mappedBy indicates that the entity in this side is the inverse of the relationship, and the owner resides in the "other" entity.
Regarding the other question of using joining tables on Non-Primary columns, there are plenty of threads why don't you go through. for example
Does the JPA specification allow references to non-primary key columns?
Is there a way to map multiple foreign keys to the same navigation property of an entity? I have a table with a self-referencing many to many relationship defined by a relationship table.
For example, I have a Person table and I want to define the different related people. I created another table, PersonRelationship, that defines those relationships with 2 foreign keys to the Person table. It doesn't matter if the person is referenced in the first or the second foreign key just that the person is in one. I would like my Person entity to have a list of all the relationships but instead it has two lists of relationships: one in which the person is in the first foreign key and another where it is the second foreign key.
How can I map these two foreign keys so that they map to the same list in the Person entity? (I am using a database first approach)
I would like to map all many-to-may relations through a single table in my database.
Meaning that I have numerous tables (entities) that have various many-to-many relations. Instead of having a separate mapping table for every relation I would like to use one "master mapping" table having to columns: End1Id & End2Id.
Don't ask why ;) It's required by my customer...
How would I set this up in the model designer, or do I have to edit the edmx xml directly....or is it just not possible?
Thanx for your help!
In such a scenario you can't have explicit foreign keys, because a table like this normally has at least three rows:
PK of table 1
PK of table 2
Type of mapping, which specifies the exact tables to use.
Because of that, you can just create a table in EF, but it will also have no connections to other tables and you will have to do the joins manually.
You would need to set this Master Mappings table manually. The designer doesn't do it for you automatically.
However - if denormalized entities are what you are looking for, better have those denormalized in DB level rather than in EF/code level.
Is it possible to create associates b/t 2 non-key fields in the Entity Framework?
Example: Take the 2 tables in a legacy application (i.e. keys/structure cannot change)
Order (
OrderId : int : PK
OrderNo : varchar
)
OrderDetails (
DetailRecordId : int : PK
OrderNo : varchar
)
In the Entity Framework, I want to create an association b/t Order and OrderDetails by the OrderNo field, which is not a primary key on either table or a FK relationship in the database.
This seems to me as not only should it be easy to do, but one reasons to use something like EF. However, it seems to only want to allow me to create associations using entity keys.
The Entity Framework allows you to claim that columns are keys and that FK constraints exist where none actually exist in the database.
That is because the SSDL (StorageModel part of the EDMX) can if necessary be manipulated by you and lie about the database.
The EF will then interact with the database as if the keys and foreign keys really do exist.
This should work, but all the normal caveats about referential integrity apply.
See my Entity Framework Tips
Hope this helps.
The problem with using non-key fields to define relationships is that the keys are not guaranteed to be properly navigatable. That could lead to a situation where you have a one to one relationship between two entities where there are more than one possible rows that fufill the relationship.
...when relating data from a database, the relationships should always be based on keys. The keys enforce the referential integrity.
One more workaround:
create view vOrder which will not include PK and create Entity from it.
Set PK in this entity to OrderNo
Now you will be able create association