Add support for Cassandra storage type.

[framirez07]

Support for the new storage type Cassandra needs to be added in the spa codegen. The following guidelines should be considered:

• Do not add support for sorting, both in the UI (React components) and in the graphql api requests.
• Enforce cursor-based-pagination for Cassandra models. Do not add support for limit-offset-pagination.
• Pagination functionality should include:
  • Forward pagination.
  • Jump to first page.
  • To be confirmed: Refresh current page using includeCursor option.
• Pagination functionality should not include:
  • Backward pagination.
  • Jump to last page.
• Search functionality should be limited to the following operators:

enum CassandraOperator{
    eq
    lt
    gt
    lte
    gte
    ne
    in
    contains   # CONTAINS
    ctk    # CONTAINS KEY
    tlt    # Token < Token
    tgt    # Token > Token
    and
}

Related issues

• Translate the SQL data model API to Cassandra (CQL) #34

Related branches

• graphql-server-model-codegen: issue34-cassandra

• graphql-server: issue34-cassandra

[coeit]

Comments from @asishallab :

1. What to do with the not associated list in the SPA in case of Cassandra stored models?
   Note, that Cassandra does not support the not operator required to populate this list.

Solution:
Display all records and warn using our Snackbar about this restriction, e.g. with "This data-model is stored using Cassandra. Technical restrictions will make associated records show up in the 'not associated' list". (Remember to I18n this message, please.)

2. What to do with search boxes for Cassandra stored data models?
   Note, that Cassandra does not support the like or or operators. We thus cannot combine a query over several fields and cannot query for sub-string matches.

Solution:
Warn the user using the Snackbar that "This data-model is stored using Cassandra. Due to technical restrictions searches in the identifier field (see key icon) using the equality operator are supported." (Remember to I18n this message, please). Implement the search using the equality operator on the identifier field.