TYPES BEGIN OF MESH — meshes

Level: 301 · deep dive

Status: stub — the shape is here; the worked program is not yet.

One line: A mesh (7.40) is a structure whose components are internal tables with declared associations between them, so that a mesh path — lo_mesh-orders\items[ ls_order ] — follows a foreign-key relationship without writing the READ TABLE — an elegant idea that almost nobody uses, and that is worth recognising when you meet it.

The shape

TYPES: BEGIN OF MESH ty_shop,
         customers TYPE ty_customers ASSOCIATION to_orders TO orders ON customer = id,
         orders    TYPE ty_orders    ASSOCIATION to_items  TO items  ON order    = id,
         items     TYPE ty_items,
       END OF MESH ty_shop.

DATA ls_shop TYPE ty_shop.
" ... fill the three tables ...
LOOP AT ls_shop-customers\to_orders[ ls_customer ] INTO DATA(ls_order).
  " orders of this customer, via the association
ENDLOOP.

Associations are declared once, in the type, and every mesh path uses them. Inverse associations (\^to_orders) walk the other way; paths chain.

Why it is on the shelf

Because it is real ABAP, because the same idea — associations declared with the data — is exactly what CDS views do on the database side, and because a reader meeting \ in a table expression for the first time has no way to guess what it means. In practice the CDS form won; meshes are rare in shipped code.

What this page still needs

• [ ] a snippets/ program with a three-table mesh and a chained path
• [ ] performance: whether a mesh path uses the table keys, measured
• [ ] the mesh forms of INSERT, DELETE and MODIFY

See also

• TYPES and CONSTANTS — where a mesh type is declared
• READ TABLE and table expressions — what a mesh path replaces
• CDS views — the same idea, on the database
• Internal tables — the tables inside the mesh