fix: starts endswith for null values (#975)

Wrap `startswith` and `endswith` with `coalesce` to return false when
element is `NULL`.

db-service/lib/cql-functions.js

@@ -75,15 +75,15 @@ const StandardFunctions = {
    * @param {string} y
    * @returns {string}
    */
-  startswith: (x, y) => `instr(${x},${y}) = 1`, // sqlite instr is 1 indexed
+  startswith: (x, y) => `coalesce(instr(${x},${y}) = 1,false)`, // sqlite instr is 1 indexed
   // takes the end of the string of the size of the target and compares it with the target
   /**
    * Generates SQL statement that produces a boolean value indicating whether the first string ends with the second string
    * @param {string} x
    * @param {string} y
    * @returns {string}
    */
-  endswith: (x, y) => `substr(${x}, length(${x}) + 1 - length(${y})) = ${y}`,
+  endswith: (x, y) => `coalesce(substr(${x}, length(${x}) + 1 - length(${y})) = ${y},false)`,
   /**
    * Generates SQL statement that produces the substring of a given string
    * @example

postgres/lib/cql-functions.js

@@ -10,8 +10,8 @@ const StandardFunctions = {
   countdistinct: x => `count(distinct ${x.val || x || '*'})`,
   contains: (...args) => `(coalesce(strpos(${args}),0) > 0)`,
   indexof: (x, y) => `strpos(${x},${y}) - 1`, // strpos is 1 indexed
-  startswith: (x, y) => `strpos(${x},${y}) = 1`, // strpos is 1 indexed
-  endswith: (x, y) => `substr(${x},length(${x}) + 1 - length(${y})) = ${y}`,
+  startswith: (x, y) => `coalesce(strpos(${x},${y}) = 1,false)`, // strpos is 1 indexed
+  endswith: (x, y) => `coalesce(substr(${x},length(${x}) + 1 - length(${y})) = ${y},false)`,
   matchesPattern: (x, y) => `regexp_like(${x}, ${y})`,
   matchespattern: (x, y) => `regexp_like(${x}, ${y})`,
 

test/scenarios/bookshop/funcs.test.js

@@ -66,6 +66,15 @@ describe('Bookshop - Functions', () => {
       expect(wrong.data.value.length).to.be.eq(0)
     })
 
+    test('not endswith finds null', async () => {
+      const { Books } = cds.entities('sap.capire.bookshop')
+      await cds.run(INSERT({ ID: 123, title: 'Harry Potter', stock: undefined }).into(Books))
+      const res = await GET(`/browse/Books?$filter=not endswith(author,'Poe')`)
+      expect(res.status).to.be.eq(200)
+      expect(res.data.value.some(item => item.ID === 123)).to.be.true
+      await cds.run(DELETE.from(Books).where({ ID: 123 }))
+    })
+
     test('indexof', async () => {
       const res = await GET(`/browse/Books?$filter=indexof(author,'Allen') eq 6`)
 
@@ -91,6 +100,15 @@ describe('Bookshop - Functions', () => {
       expect(wrong.data.value.length).to.be.eq(0)
     })
 
+    test('not startswith finds null', async () => {
+      const { Books } = cds.entities('sap.capire.bookshop')
+      await cds.run(INSERT({ ID: 123, title: 'Harry Potter', stock: undefined }).into(Books))
+      const res = await GET(`/browse/Books?$filter=not startswith(author,'Poe')`)
+      expect(res.status).to.be.eq(200)
+      expect(res.data.value.some(item => item.ID === 123)).to.be.true
+      await cds.run(DELETE.from(Books).where({ ID: 123 }))
+    })
+
     test('substring', async () => {
       const [three, two, negative] = await Promise.all([
         GET(`/browse/Books?$filter=substring(author,1,2) eq 'dg'`),