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.
Column-oriented layout of a user interface with columns in each row
The next sections give some more detailed information on the run time semantics for CRUD annotations as implemented in Ampersand.
Create
CRUD
for a box
for a field.
C
​
 A + (plus) button is displayed that lets you create a new atom, but only if the box-expression is editable.
​
 Enter a new atom and a + button appears. Click the + to add that atom to the listed set of atoms. If you enter an atom that exists (Peter), you can select it.
c
Atoms cannot be created
Atoms cannot be created
Read
Read
CRUD for boxes
​
CRUD for fields
R
Read is allowed
​
Read is allowed
r
Read is not allowed
​
Read is not allowed
Update
Update
CRUD for boxes
CRUD for fields
U
​
 Removing and/or adding a pair (src,tgt) is allowed if expr is editable and the atom exists. Deleting a pair is done with the - button; the atom will NOT be deleted.
​
 Removing and/or adding a pair (src,tgt) is allowed if expr is editable and the atom exists. Deleting a pair is done with the - button; the atom will NOT be deleted.
u
Update is not allowed
Update is not allowed
Delete
Delete
CRUD for boxes
CRUD for fields
D
​
 Deleting a pair is done with the - (minus) button. Deleting an atom is done with the trash bin.
​
 Delete atom (tgt) and all pairs in which it is used.
d
delete not allowed
delete not allowed
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.

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Last modified 2yr ago

CRUD	for a box	for a field.
C	A + (plus) button is displayed that lets you create a new atom, but only if the box-expression is editable.	Enter a new atom and a `+` button appears. Click the + to add that atom to the listed set of atoms. If you enter an atom that exists (Peter), you can select it.
c	Atoms cannot be created	Atoms cannot be created

Read	CRUD for boxes	CRUD for fields
R	Read is allowed	Read is allowed
r	Read is not allowed	Read is not allowed

Update	CRUD for boxes	CRUD for fields
U	Removing and/or adding a pair (src,tgt) is allowed if expr is editable and the atom exists. Deleting a pair is done with the - button; the atom will NOT be deleted.	Removing and/or adding a pair (src,tgt) is allowed if expr is editable and the atom exists. Deleting a pair is done with the - button; the atom will NOT be deleted.
u	Update is not allowed	Update is not allowed

Delete	CRUD for boxes	CRUD for fields
D	Deleting a pair is done with the - (minus) button. Deleting an atom is done with the trash bin.	Delete atom (tgt) and all pairs in which it is used.
d	delete not allowed	delete not allowed