CRUD

CRUD annotations are used in services to constrain the functionality of fields and boxes in an INTERFACE-statement. This allows you to minimize the functionality for your users, to design for easy learning.

Each CRUD annotation comes right after a term, so we can always refer to "the term" to which a CRUD annotation belongs. A CRUD annotation constrains the things your user can do with the target atoms and the pairs of its term.

The CRUD-annotation specifies Create, Read, Update, and Delete rights for the term it follows. Capital = allowed, Non-capital = not allowed. CRUD is the default, so if you specify nothing, everything is allowed. The following service definition illustrates this.

INTERFACE Overview : "_SESSION"                  cRud
BOX <TABS>
     [ Students : V[SESSION*Student]             cRuD
       BOX <TABLE>
                [ "Student" : I[Student]         cRud
                , "Enrolled for" : isEnrolledFor cRUD
                , "Course" : takes CRUD
                ]
     , Course : V[SESSION*Course]                cRuD   -- used for a box
       BOX <TABLE>
                [ "Course" : I                   cRud   -- used for a field
                , "Modules" : isPartOf~                 -- CRUD is default
                ]
     , Modules : V[SESSION*Module]               cRud
       BOX <TABLE>
                [ "Modules" : I                  cRuD
                , "Course" : isPartOf            cRUd
                , "Students" : isEnrolledFor~    CRUD
                ]
     ]

The user interface defined by this service is shown as a screenshot below. Notice that the lowercase r in the annotation of the Students box prevents showing the underlying box. The full CRUD functionality in Course yields 'create' functionality (the green plus-button), 'remove pair' functionality (red minus button), and 'delete atom' functionality (the red trash can button). The lowercase c, u, and d in the Modules box prevents displaying that functionality in the user interface.

The next sections give some more detailed information on the run time semantics for CRUD annotations as implemented in Ampersand.

Create

Read

Update

Delete

A top-level Update or Create are common in my own scripts, e.g. to create an overview of People and be able to create a new Person: INTERFACE "People" : V[SESSION*Person] CRud COLS []. And update is also possible.

Things to remember

1. The red minus is enabled by U. It unlinks an atom (by deleting a pair from a relation) and leaves the atom alone.

2. The red trash bin is enabled by D. It removes an atom and all pairs in which that atom is used.

Background

Motivations for CRUD-functionality are found in the GitHub discussions on CRUD functionality.