Fix event model association which are doing multiple queries

[ashwinisukale]

Recommendation: Refactor model relationships. Cost: 3/5 Benefit: 4/5
We have a number of relationships mapped to the same table e.g DoiModel:

has_many :view_events, -> { where target_relation_type_id: "views" }, class_name: "Event", primary_key: :doi, foreign_key: :target_doi, dependent: :destroy
 has_many :download_events, -> { where target_relation_type_id: "downloads" }, class_name: "Event", primary_key: :doi, foreign_key: :target_doi, dependent: :destroy
 has_many :reference_events, -> { where source_relation_type_id: "references" }, class_name: "Event", primary_key: :doi, foreign_key: :source_doi, dependent: :destroy
 has_many :citation_events, -> { where target_relation_type_id: "citations" }, class_name: "Event", primary_key: :doi, foreign_key: :target_doi, dependent: :destroy
 has_many :part_events, -> { where source_relation_type_id: "parts" }, class_name: "Event", primary_key: :doi, foreign_key: :source_doi, dependent: :destroy
 has_many :part_of_events, -> { where target_relation_type_id: "part_of" }, class_name: "Event", primary_key: :doi, foreign_key: :target_doi, dependent: :destroy
 has_many :version_events, -> { where source_relation_type_id: "versions" }, class_name: "Event", primary_key: :doi, foreign_key: :source_doi, dependent: :destroy
 has_many :version_of_events, -> { where target_relation_type_id: "version_of" }, class_name: "Event", primary_key: :doi, foreign_key: :target_doi, dependent: :destroy

This results in too many queries to the database. Ideally, we want to have a single association for events with various conditions. This will require refactoring of places where we are using these associations.

The above is just one example, the recommendation is to do this for other associations like these in other models.