Basically I have an entity that contains food dishes and another that contains wine. Each dish has wine recommendations. I need to be able to select a dish and see the wine recommendations that come with that dish. Different dishes can have the same wine recommended for it.
Normally in SQL I would create a link table to achieve this but I am a bit stumped here, can anyone help?
Core Data handles the details of "to-many" relationships under the hood for you, you don't need to make intermediary tables.
Open your Core Data .xcdatamodel file, select the Food Entity, and click Add Relationship. Name the relationship wines. Make its destination entity the Wine entity. Open the Data Model Inspector (option-cmd-3) and select To-Many Relationship.
Now select the Wine entity. Create a relationship called foods. In the Data Model Inspector make the relationship's Desination the Food entity, it's inverse relationship is wines and set it to be a To-Many Relationship as well.
Now each instance of Food can have many Wines and each instance of Wine can have many Foods.
If you are using Core Data, then you can simply create a Wine table in the database and use it's primary key as the foreign-key in the food-dishes table. What is not working in this design?
Related
I am trying to learning Database Design and trying to identify the relationship between entities.
For example Stores and Items have many-to-many relation as a store have many items and an item is sold at many different stores.
And items and reviews have one-to-many relation. now I want to identify the relation between a store and a review. How should I understand/identify such kind of relationships?
Is there a standard way in CUBA to modelize attributes for many-to-many association ? Documentation omits the topic so I guess it is not. In this case, is this in the roadmap ?
For many-to-many association (e.g between Products and Providers), CUBA Studio generates automatically a link table (holding Provider ID and Product ID).
In order to handle specific attributes to this association (e.g Boolean preferredProvider) it would need to add the preferredProvider column in the link table and create a class holding the two IDs and the attribute.
It would also probably impact the platfom mechanism of fetching many-to-many associations.
I'm reasonably sure that CUBA Studio does not manage it as of 2.2.3 - no option in Studio GUI, nothing in doc. It is still of course possible to code the case manually but one would need to manually write JPQL. Not necessarily a big deal but losing a strong feature of the platform here just for one field.
So I created the preferredProvider field as a one-to-one association from Product to Provider, which is a valid workaround at the cost of an additional association.
I want to create a Entity which can hold fields which will be dynamic
Let's say I have a Entity named Party and another entity named People, each party can hold N number of people names
How should I create such record?
Is there any other way other than creating fields like People1, People2 as lookup to the people entity?
You should look what N:N relationship is. You will not have exactly fields but you will have possibility to put subgrid of People type to Party entity to know what People belong to this Party and vice versa.
BizAgi tables are used to view collections in 1-m relationships.
It is also possible to view m-m relationships from the point of view of one entity (thus, a 1-m relationship).
The add and delete buttons don't work with m-m relationships and no errors appear.
Has anybody used them successfully?
My interpretation with an example:
One contract has N clients, and one client has N different contracts. You want to use collections to represent this connection.
The only was I see of representing this information is to have a table of contracts, to which the edit/detail form shows a table of clients for that contract.
You might also want to consider using a form link as a column of that table.
Let me know if this is a correct interpretation.
I've not really used access for a while and not too sure how best to proceed with this data model:
I have set of resource tables of differing type, eg: Data, Literature, Contractors, etc.
I also have a set of category tables such as Procedures, Topics, and Regions.
I need to create many-to-many relationships between the various resources and the various categories so it is possible to view a resource record and see lists of the various categories to which the resource is allocated, and vice-versa, that is to view all resources allocated to a specific category.
I realise that I could create lots of link tables, eg: LnkDataProcs, LnkDataTopics, etc, however with perhaps 10 resource tables and 3 category tables I would wind up with 30-odd link tables which seems wrong (it may also be useful to query all resources from each category anyway so it would be good to have one link table for each category).
I've done this kind of thing before using SQL in custom DB client apps by using one link table with fields as follows: CategoryTable, CategoryID, ResourceTable, ResourceID - So that the link table stores the table name as well as the foreign key.
However I'm not too sure how to fit this kind of model into an access database, it would be nice to use the Access framework (master-child form objects) rather than having to write loads of custom code to perform queries and populate forms.
Any ideas how to proceed, or even what this kind of relationship is called?