2016年6月26日 · This is my standard way of specifying foreign keys which works for all cases EXCEPT when an entity contains more than one nav property of the same type (similar to the HomeTeam and GuestTeam scenario), in which case EF gets confused in generating the SQL. Solution is to add code to OnModelCreate as per the accepted answer as well as the two collections for both sides of the relationship.

2010年4月29日 · A relational model diagram will use lines between boxes for visual purposes, but a complete attribute list will include these foreign keys. Another difference between ER modeling and relational modeling is that in relational modeling, a many-many relationship will be diagrammed as a box with two (or more) lines leading up to it.

I presume that you refer to FKs in fact tables. During DW loading, indexes and any foreign keys are dropped to speed up the loading -- the ETL process takes care of keys. Foreign key constraint "activates" during inserts and updates (this is when it needs to check that the key value exists in the parent table) and during deletes of primary keys in …

2008年9月17日 · FKs give a pretty big hint on what statistics are most important to collect on the database, which in turn leads to better performance they enable all kinds of auto-generated support -- ORMs can generate themselves, visualization tools will be able to create nice schema layouts for you, etc.

I want to limit the options of 'ganador', which is a foreign key to the Jugador model, to the foreign keys of the 'jugadorA' and 'jugadorB' fields, which also point to the Jugador model.

2017年12月1日 · I'm having trouble wiring up a working queryset to obtain all the Messages that belong in a chat room. Two users, or Profiles, make up a Pair object, which should relate to a Room--representing a c...

I'm using Entity Framework 4 with the POCO code generation template from Microsoft downloaded from the Visual Studio gallery. I am also leaving the default option to "Include foreign keys in model"

2017年12月4日 · This would involve somehow including two __str__ representations in the same model form. I have seen label_from_instance used in overriding the model form, but this looks like it's only possible with ModelChoiceFields.

2015年5月25日 · Recently i have resolved my issue, problem was i had a main table which has a primary key, and that primary key was mapped with my missing table's column in that column i set "Allow null", as i changed "Allow not null", and update my data model from Entity framework 5.0, it was visible in my solution. Thank you for all suggestions.

2017年12月11日 · But some just create a composite primary key. Conversion of an ER model into a relational model is relatively mechanical, but non trivial. And if you become good at both models, you may find it to your advantage to use the ER model for analysis of the subject matter and the relational model for database design.