Difference between relations and collections in hybris?

Question

I am new to hybris, What is diff b/w relations and collections, why we go for relations instead of collections.

Answer 1

Basically, there are two technically different ways of modeling collections in hybris:

1. CollectionTypes

   • Think of CollectionTypes in hybris as a backpack mounted onto a type
   • By runtime, CollectionTypes are resolved into a Collection of a kind of item, such as a List of MediaModels
   • Can cause overflow, resulting in truncation and therefore loss of data
   • More difficult to search and lower performance
   • On the database level, CollectionTypes are a comma-separated list of PKs, so there is a maximum

2. RelationTypes

   • Create links between all kinds of types Create type-safe n-to-m relations: Only link such elements of the source / target type declared at the relation
   • Values for relations are stored in a separate database table +Each value is stored in a separate table row

Answer 2

I'm totally agree with @KilleKat comment, he has mentioned all the differences between CollectionType and RelationType in Hybris.

I attached bellow some diagrams to have a more clearer view about the subject.

CollectionTypes: (to be used wisely)

RelationTypes: (recommended)

Answer 3

As Sumit says above,

CollectionType is discouraged and RelationType should be used whenever possible. This is because, the maximum length of the database field of a CollectionType is limited and a CollectionType with many values may end up getting its values truncated. In addition, the values of CollectionTypes are written in a CSV format and not in a normalized way. By consequence, hybris recommends using RelationTypes whenever possible.

• CollectionType: CollectionTypes are based on the Java Collection class i.e. a Collection is a list of elements.
  1:n - Keep links to the respective values via an attribute on the source item, for example, a list of Primary Keys.
  n:1 - Store the attribute values at the respective target items and have a getter method at the source type to retrieve the values.
• RelationType:
  n:m - Internally, the elements on both sides of the relation are linked together via instances of a helper type called LinkItem. LinkItems hold two attributes, SourceItem and TargetItem, that hold references to the respective item.

For each entry within a relation (in other words, for each link from one item to another), there is a LinkItem instance that stores the PKs of the related items. LinkItem instances are handled transparently and automatically by the platform: On the API level, you only need to use the respective getter and setter methods.

Answer 4

Its important to understand hybris strongly discourages using collections, use relations instead.

As stated above collections are maintained as comma separated from a data structure prospective and thats why you might see problem of data truncate, where as relations have rational data structure of creating a new table and map table to join the two table.

Collection because of there storage structure - can't be searched.

I would say for a very simple (1:n) relationship with limited data - you can still use collections. While for any complex (m:n /1:n) relationship always use relations