Support NOT NULL attribute key for erDiagram syntax

[gvenzl]

Proposal

Mermaid.js should add the attribute key NN for erDiagrams to model NOT NULL database columns.

NOT NULL is a widely used concept in relational databases to enforce the existence of a value for a field. Mermaid already supports PK, FK and UK, for Primary Key, Foreign Key and Unique Key attributes (https://mermaid.js.org/syntax/entityRelationshipDiagram.html#attribute-keys-and-comments) yet does not provide any facility to mark a column NOT NULL other than manually typing a comment for it, i.e.:

erDiagram
    BOOKS {
        int    id     PK "NN"
        string title     "NN"
        int    isbn      "NN"
        date   published
        string genre
    }

The changes look fairly isolated to

mermaid/packages/mermaid/src/diagrams/er/parser/erDiagram.jison

Line 31 in cb2bc2a

<block>\b((?:PK)|(?:FK)|(?:UK))\b return 'ATTRIBUTE_KEY'

Example

The new syntax would look like this:

erDiagram
    BOOKS {
        int    id         PK NN
        string title         NN
        int    isbn          NN
        date   published
        string genre
    }

Marking id, title and isbn all NN as NOT NULL.

Screenshots

Current, as comment approach:

[tomperr]

It's a simple improvement: as you explained, just change the grammar (and also add tests, examples and documentation about it) to allow "NN". I'm just wondering whether "NN" for "Not Null" is clear enough. "PK", "FK", "UK" are common abbreviations, but I'm not sure about "NN" (I'm not a native English speaker, so that might explain my point of view).

[Haratsu]

It's a simple improvement: as you explained, just change the grammar (and also add tests, examples and documentation about it) to allow "NN". I'm just wondering whether "NN" for "Not Null" is clear enough. "PK", "FK", "UK" are common abbreviations, but I'm not sure about "NN" (I'm not a native English speaker, so that might explain my point of view).

NN is quite common as SQL standard uses "NOT NULL" keyword to indicate the behaviour. A (more complex) solution would be to add a column "Nullability" with values "Yes" / "No", but personally I do not see any benefit on adding a column for binary labels.

In general you might need to think about "custom" or "optional" attributes, As there are plenty depending on which RDBMS is used, like e.g. "Autovalue" (MSSQL). But going that direction might end up in a bottomless pit.

[NikolayShakin]

I would add AI for the auto-increment attribute as well

[jjoaovitor7]

Discussion related: #3718