assoc2many-ambiguous-key

Rule Details

In general an association/composition to/of MANY that targets an entity without ON condition is not allowed (as it is an n:1 relationship). Here, one should always specify an ON condition following the canonical expression pattern <assoc>.<backlink> = $self. The backlink can be any managed to-one association on the many side pointing back to the one side.

Examples

✅   Correct example

In the following example, we define a unique association from Authors to Books with a well-defined ON condition and backlink, thus satisfying the rule's conditions:

db/schema.cds

namespace sap.capire.bookshop;

entity Books {
  key ID : Integer;
  @mandatory title  : localized String(111);
  @mandatory author : Association to Authors;
}

entity Authors {
  key ID : Integer;
  @mandatory name : String(111);
  books  : Association to many Books on books.author = $self;
}

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❌   Incorrect example

If we extend this example by creating a view AuthorView with a key ID and the element bookIDs without an ON condition, the rule is triggered since the key is no longer unique and bookIDs leads to multiple entries:

db/schema.cds

namespace sap.capire.bookshop;

entity Books {
  key ID : Integer;
  @mandatory title  : localized String(111);
  @mandatory author : Association to Authors;
}

entity Authors {
  key ID : Integer;
  @mandatory name   : String(111);
  books  : Association to many Books on books.author = $self;
}

view AuthorView as select from Authors {
  // Ambiguous key in 'AuthorView'. Element 'bookIDs' leads to multiple
  // entries so that key 'ID' is not unique.
  key ID, 
  books.ID as bookIDs
}

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Version

This rule was introduced in @sap/eslint-plugin-cds 1.0.1.