I am using SQL Server database and Django. I have a Database named as Person Database and Other database as Student Database. In Person database I created models, but in Student database there are no models because the tables and data are already existing. So I am getting data of Student database using Pyodbc. Now I am creating a new model in Person database where I need to create a foreign key for student database. Can anyone help me out how to do it.
You cannot create a Foreign Key relation in between tables of different databases. Foreign Key relations can only be created between tables of the same database. There is a workaround on this, although it is not recommended. Please refer this answer.
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I want to create master data for an organization. I have 5 basic data, one of them is persons. I use the master data service (SQL server). I designed models with the named party and some entities. my entities are Person, organization and Source_relation and another domain base table. I have an attribute in the source_relation table that shows a code. each party has a code and it is in the source_relation table. The person and organization have FOREIGN KEY to source_relation entity. how to design this in master data service? using a unique identifier for the relation between these tables are correct?
Yeah, that will wise to use FOREIGN KEY to connect between two tables.
I have a database and i want to generate ER (entity relationship) diagrams
for the database. I have tables and foreign key relation to the other tables
how to mention these relation ship in my ER diagrams?
I am new to ER diagrams can you tell me?what is the best way to design?
can u tell me ER diagrams only for database?
I have one table it contains nearly 32 fields all the fields is mandatory to
mentioned in ER diagram?
You can check This Link for your query , by this link these are the steps.
Follow these steps.
1.Go to Sql Server Management Studio ->Object Explorer->Databases->Database Node(The node which will have your databse name).
2.Under your database node you will find a node named Database Diagrams along with node for Tables,Views etc.
3.Right Click on "Database Diagrams" node and select new database diagram and it will launch a wizard to generate Database diagram.
This Diagram will contain all tables along with their keys and relationships.
Using EF6, I have two tables in an SQL database and I've used database first to create the EF diagram from the database.
My database is missing a foreign key constraint between the PK of one table and a foreign key in the other.
Rather than add the foreign key constraint into the database I created it as an association in the EF model.
The association looks good in the EF model, it has the correct principal and dependant.
However if I delete a row from the principal table when dependants are present, referential integrity doesn't kick in and the principal row gets deleted.
I know I can just add the relationship into the SQL database and update model from database. But I'd like to understand the scope of functionality of EF and whether it should be possible to add a relationship in the EF model but not in the SQL database and for it to still work?
It seems to me that if the association (relationship) exists in EF but not in MSSQL, then the association is ignored for referential integrity when you delete a row via EF?
However if I delete a row from the principal table when dependents are present, referential integrity doesn't kick in and the principal row gets deleted.
Dependents are present in database, or are present in Context?
If you haven't loaded all the dependent entities in the context, there is no way for EF to delete them. It needs their key for the delete statement. It doesn't even know they exist if they are not in the context.
So, the only way for referential integrity to work would be if EF retrieves all related entities into the context, on delete of principal entity, so it could issue a delete statement for every one of them (even if there are thousands).
I think, though, if there are dependent entities present in context, EF will issue delete statement anyway (even if it expects db to do all the work).
Hope it helps.
I'm distributing a database but I have two tables with foreign keys references to the other database in other server. I have already searched and found that I can't make a foreign key referring to a table in another database in other server. But, how can I resolve this problem? Creating views?
In the instance that needs to refer to "the other server", introduce "the other server" as a linked server and then use INSTED OF triggers to validate the FK constraints.
I am working on an old database, that i do not want to touch or modify in any way if possible.
I want to build a new application that uses it's data but the database has no actual relations despite having primary and foreign keys linking tables.
If i import these tables into an Entity Framework model and add the associations manually, will i be able to use things such as lazy loading and linq?
Many thanks,
Kohan
This is definitely possible. Entity Framework simply generates SQL queries containing joins or where clauses that reference columns that you define in your conceptual model as foreign keys. The generated SQL is directly executed by the database.
Primary and foreign keys are only in your database for referential integrity. As a very simple test you can execute a SQL statement directly in your database that joins two related tables that do not have a foreign key relationship. You'll see that the query simply works. Entity Framework does exactly the same when you correctly define the relationships in your model.