yaml Using anchors and aliases for transcluded content Using YAML aliases to cross-reference rows from a YAML table

Example

    ---
    person_table:
      - &person001
        fname:  homer
        lname:  simpson
        role:   dad
        age:    33

      - &person002
        fname:  marge
        lname:  simpson
        role:   mom
        age:    34

      - &person003
        fname:  peter
        lname:  griffin
        role:   dad
        age:    34
        
    motto_table:
      - &motto001
        person:   *person001
        motto: >
          D'oh!! YAML is too complicated!

      - &motto002
        person:   *person002
        motto: >
          Bart! Listen to your father!

      - &motto003
        person:   *person003
        motto: >
          Hey! YAML is freakin' sweet!

Problem

• developer wishes to cross-reference rows-with-anchors from one table and link to them with rows-as-aliases in another table

Solution

• use YAML aliases, which cross-reference pre-defined anchors from another table
• in YAML, reusable "transclusion identifiers" are called anchors and aliases
• in YAML, reusable "transclusion identifiers" consist of alphanumeric tokens preceeded by an ampersand or asterisk

Rationale

• YAML anchors and aliases allow for increased data normalization
• YAML anchors and aliases enforce DRY (Don't repeat yourself)
• in this example, a table structure can be designed and preserved which closely coincides with a database
• in this example, data entry and file sizes can be reduced

Pitfalls

• in this specific example, yaml.load() will produce nested dictionaries
  • this is referred to as the "nested dictionaries problem"
  • under the person name-value pair, the value for person will be a sub-dictionary
  • this may be undesirable, because it breaks the uniformity of the table structure
• failure to correctly specify aliases will result in missing data
  • (typos will create broken cross-references)
• YAML does not support file transclusion by reference, so all aliases and anchors must exist in the same yaml file
• not all YAML parsers reliably support anchors and aliases

See also

Stackoverflow YAML