page_title: Many-to-many (data model)
hierarchical_section_title: Many-to-many (data model)
caption_attribution_description: English: A many-to-many relation implemented as two one-to-many relationships with a junction table.
context_page_description: In systems analysis, a many-to-many relationship is a type of cardinality that refers to the relationship between two entities A and B in which A may contain a parent instance for which there are many children in B and vice versa.
  For example, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors.
  In a relational database management system, such relationships are usually implemented by means of an associative table, say, AB with two one-to-many relationships A -> AB and B -> AB. In this case the logical primary key for AB is formed from the two foreign keys.
  In web application frameworks such as CakePHP and Ruby on Rails, a many-to-many relationship between entity types represented by logical model database tables is sometimes referred to as a HasAndBelongsToMany relationship.
context_section_description: In systems analysis, a many-to-many relationship is a type of cardinality that refers to the relationship between two entities A and B in which A may contain a parent instance for which there are many children in B and vice versa.
  For example, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors.
  In a  relational database management system, such relationships are usually implemented by means of an associative table (also known as join table, junction table or cross-reference table), say, AB with two one-to-many relationships A -> AB and B -> AB. In this case the logical primary key for AB is formed from the two foreign keys (i.e. copies of the primary keys of A and B).
  In web application frameworks such as CakePHP and Ruby on Rails, a many-to-many relationship between entity types represented by logical model database tables is sometimes referred to as a HasAndBelongsToMany (HABTM) relationship.
caption: The Author-Book many-to-many relationship as a pair of one-to-many relationships with a junction table
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