Rudimentary tree support for Genres on SQLite

fiori/server.js

@@ -1,17 +1,32 @@
-const cds = require('@sap/cds')
-cds.on('served', () => {
-  // register a simplified handler for tree table
-  // no filtering/searching/collapsing/expanding of nodes
-  if (cds.db.kind === 'sqlite') {
-    const { AdminService } = cds.services
-    AdminService.prepend(() => {
-      AdminService.on('READ', 'Genres', (req,next) => {
-        const { SELECT } = req.query
-        // Suppress error message: Feature "recurse" queries not supported.
-        delete SELECT.__proto__.recurse
-        delete SELECT.recurse
-        return next()
-      })
-    })
-  }
-})
+const cds = require('@sap/cds/lib')
+if (cds.requires.db.kind === 'sqlite') {
+
+  // Add a column to the Genres table, to efficiently determine if a node
+  // is a leaf, and use it for DrillState in hierarchy queries.
+  cds.on('loaded', m => Object.assign (
+    m.definitions['sap.capire.bookshop.Genres'].elements,
+    cds.parse (`entity Genres {
+      DrillState: String = coalesce(leaf,'collapsed');
+      leaf: String;
+    }`).definitions.Genres.elements
+  ))
+
+  // Fill in `leaf` helper column for initial data entries
+  cds.on('served', ()=> cds.run(`
+    UPDATE sap_capire_bookshop_Genres as g SET leaf='leaf' WHERE not exists (
+      SELECT 1 from sap_capire_bookshop_Genres WHERE parent_ID = g.ID
+    )`
+  ))
+
+  // Register a simplistic handler for hierarchical queries
+  cds.on('serving:AdminService', srv => srv.prepend(() => srv.on('READ', 'Genres', (req,next) => {
+    const q = req.query, parent = {ref:['parent','ID']}
+    if (q.SELECT.recurse?.where?.[0].ref[0] === 'Distance') q.SELECT.where[0] = parent
+    else if (!q.SELECT.search) q.SELECT.where ??= [ parent, 'is null' ]
+    // Suppress error message: Feature "recurse" queries not supported.
+    delete q.SELECT.__proto__.recurse
+    delete q.SELECT.recurse
+    return next()
+  })))
+
+}