I have the following Table Structure
Facility
PK Facility ID
AccountID
Accounts
PK NameID
PK AccountID
I can't touch the DB so my changes need to be in Entity Framework. Essentially the AccountIDs are linked so I want to create an association between them. So when I create an association I map the AccountIDs together, however I can't map FacilityID to anything and NameID to anything so when I save Visual Studio complains that the mapping is not set correctly.
My main question is how do I ignore the mappings for FacilityID and NameID? I've tried added [NotMapped] to both FacilityID and NameID but that does not work. I've also tried creating a scalar property for Facility and Accounts and used the Referntial Constraint to map them however when I try to map the columns under Table Mapping, the columns I added do not show up which causes VS to complain as well.
Here is my table, I removed most of the fields because they are unnecessary
Assuming Account.AccountID is unique (ie no two rows in Account actually have the same AccountID), just declare that as the only Key Property on the Account entity.
The Key of an entity does not have to be declared as the PK in the database. But you can only have one Key per entity (the Key can, of course, have multiple columns, and EF Core does support alternate keys). The entity Key should be unique, and should have a unique index in the database on the corresponding columns, but that's not enforced by EF.
Related
I have two tables:
User table with primary key UserId.
Follow table with primary key FollowId.
The Follow table has a column called FollowedId which can mean the primary key of several entities, including User, Keyword, City, Business etc.
There is an additional column in the Follow table called FollowedTypeId, this indicates which entity the FollowedId represents.
How can I create a navigation property on the User table and have that automatically populated with all it's related entities in the Follow table?
I've been looking up composite keys and how to map but I'm afraid I've not yet been able to understand how to accomplish this.
I've created an edmx for my database. In it Entity framework removed a table and instead created an association between two tables because it matches a column name with the primary key in the other table.
I do not want that as there is no real association between those tables. How can I remove that association and get a class for the middle table instead?
Example:
SomeTable
Id int pk
MiddleTable
SomeTableId int fk
SomeCode int
OtherTable
SomeCode int pk
It's the MiddleTable which do not get a class.
Remove one table from the edmx, e.g. OtherTable.
Update model from database and add MiddleTable.
Update model from database and add OtherTable.
When I do this with a similar model I end up with an association between SomeTable and MiddleTable and an unassociated OtherTable. Now you can add/remove associations manually as you wish.
It's normal EF behavior not to create a class for the middle table. This is a so-called many to many association between SomeTable and OtherTable which can be modelled by two collection properties:
SomeTable.OtherTables
OtherTable.SomeTables
The middle table, the junction table, is not really necessary.
It's a bit surprising to me that you say that there is no association between the two tables although, apparently, in the database there are foreign keys. Technically, it is a many to many association.
I have a program using Entity Framework (EF) Database First in the data access layer. I know that in order for EF to auto-generate the navigation properties of a many to many relationship, the mapping table needs to contain only a composite primary key:
Project
- ProjectId (PK)
- Name
ContentType
- ContentTypeId (PK)
- Name
ProjectContentTypeMapping
- ProjectId (PK)
- ContentTypeId (PK)
In this case everything works fine, and I can access Projects from ContentTypes and the other way around with navigation properties.
However I have a requirement to have extra fields that are particular to the relation between Projects and ContentTypes, and that would be extra columns in the ProjectContentTypeMapping table. Once I add these I loose the navigation properties, and EF shows the mapping table in the designer.
Is there any way I can manually configure the mapping between these two tables in EF (Database First)? Alternatively, how can I represent this? I was thinking of maybe having an extra "metadata" table with a FK to the mapping table, but it looks "hacky" to me...
Thanks
No, you cannot have extra columns in your mapping table in entity framework.
Because, having an extra column implies you intend to use it, but Mapping tables are not part of the entity, so, entity framework, no longer treats your mapping table with extra columns as a Mapping table. You will have to manipulate the Mappings manually.
Lets take example of your classes:
Project
- ProjectId (PK)
- Name
- ProjectContents
ContentType
- ContentTypeId (PK)
- Name
- ProjectContents
ProjectContentTypeMapping
- ProjectId (PK)
- ContentTypeId (PK)
- OtherRelevantColumn
where ProjectContents is of type ProjectContentTypeMapping
so whenever you add a Project with Certain ContentType, you would be doing this:
Project prj = new Project();
//fill out scalar properties
ProjectContentTypeMapping pctm = new ProjectContentTypeMapping();
pctm.ContentTypeId = 1; //or whatever you want, or selected from UI
prj.ProjectContents = new ProjectContentTypeMapping();
prj.ProjectContents.Add(pctm);
dataContext.Projects.Add(prj);
Now in case of editing (adding ContentTypes) to an existing project, you won't do prj.ProjectContents = new ... rather, you would do it only when it is null i,e,
if(prj.ProjectContents==null)
prj.ProjectContents = new ProjectContentTypeMapping();
also, one very very important thing, since now your ProjectContentTypeMapping is no longer a mapping table, so, deleting a Project would give you an error, if its id is being present in ProjectContentTypeMapping table; you will have to remove them manually i.e
foreach(var pctm in prj.ProjectContents.ToList())
{
prj.ProjectContents.Remove(pctm);
datacontext.ProjectContentTypeMappings.Remove(pctm);
}
datacontext.Remove(prj);
datacontext.SaveChanges();
I have the following tables:
Table Group (
id INT PK,
year INT PK,
name VARCHAR
)
Table Person (
id PK,
GroupID INT,
name VARCHAR
)
The database does not have foreign keys defined so I want to create a manual association from the Person tables GroupID to the Group tables id.
To do this I right click Person and Add an association. I create a Many to One association and everything works. The problem is when I go to add the mapping. Because the Group table has two primary keys entity framework was something from the Person table to map to the year key.
What do I need to do to create the association?
You cannot create such association because EF follows same rules as database. All PK columns from principal entity must exists as FK columns in dependent entity.
The only way can be some database view selecting distinct Groups with Id and Name and mapped as read only entity and build navigation between those two. I didn't try it but I guess it should work. It will have its own disadvantages because you will have two completely unrelated entities for group and the entity related to person will not accept any modification (without mapping custom SQL commands or stored procedures to insert, updated and delete operations).
I have a database with multiple tables, and some basic relationships. Here is an example of the problem I am having:
My Database:
**Org**
ID
Name
etc
**Detail1**
ID
D1name
**Org_Detail1**
Org_ID
Detail1_ID
**Detail2**
ID
D2Name
**Org_Detail2**
Org_ID
Detial1_ID
BooleanField
My problem is, the Org_detail1 table is not showing up in the entity model, but the Org_Details2 table does.
I thought it may have been because the Org_Detail1 table only contains two ID fields that are both primary keys, while the Org_Details2 table contains 2 primary key ID fields as well as a boolean field.
If I add a dummy field to Org_detail1 and update it, it still won't show up and wont allow me to add a new entity relating to the Org_Detail1 table. The table won't even show up in the list, but it is listed under the tables.
Is there any solution to get this table to appear in my model?
Seems like I may just need to completely delete the model and recreate it. Adding dummy fields is the only solution I've found.
Not sure this is an MVC problem.
Does a Detail1 collection turn up in your Org entity and an Org collection show up in your Detail1 entity. This is the normal behaviour for Entity framework for a many to many intersecting table with no other tangible data.
If not then maybe the foreign key constraints are not defined.