Search code examples
intersystems-cache

Does SQL Table name === Class name? and vice-versa?

So I'm just learning Cache, and have a question about tables, classes and globals, what's the difference?

I'm doing the tutorial and it seems like, since this is an object-orientated DB that a class is a table and vice versa. So if I create a class and make it persistent with properties, I can use SQL to query it. Is this true? What's a global then?

Reason I ask is because I'm using Management portal for one of our Cache applications and although I can see a table in WinSQL and Documatic, that same table doesn't seem to exist in the class explorer (Under management portal)... can't figure it out, is it hidden? Is there a command to see class def'ns in terminal??

thanks!

Solution

  • In Caché, classes are tables and tables are classes. You can choose when you want to use SQL access and when you want to use Object Oriented access.

    Globals are the sparse multidimensional arrays which sit as storage beneath the class/table. Look at the storage definition at the end of your class to see the actual globals that your persistent class is stored in (e.g. ^Sample.PersonD)

    By default, class names are projected as table names, but there are some rules which apply in order to ensure that the table names comply with SQL standards:

    • if you have a class that is a couple of packages deep (e.g. MyApp.Data.Person) then all but the last "." will be replaced by "_" in the table name (e.g. MyApp_Data.Person would be the table name)
    • You can't use reserved SQL keywords in table names, so if you make something in the User package for example (class: User.Person) then Caché will change the Package name (e.g. SQLUser.Person would be the name of the table)

    I suggest you refer to http://docs.intersystems.com/cache20141/csp/docbook/DocBook.UI.Page.cls?KEY=GORIENT_ch_persistence for more detail