fix: #3513, hasMany relationships unable to be cleared

packages/db-postgres/src/transform/read/traverseFields.ts

@@ -215,7 +215,19 @@ export const traverseFields = <T extends Record<string, unknown>>({
 
       if (field.type === 'relationship' || field.type === 'upload') {
         const relationPathMatch = relationships[`${sanitizedPath}${field.name}`]
-        if (!relationPathMatch) return result
+        if (!relationPathMatch) {
+          if ('hasMany' in field && field.hasMany) {
+            if (field.localized && config.localization && config.localization.locales) {
+              result[field.name] = {
+                [config.localization.defaultLocale]: [],
+              }
+            } else {
+              result[field.name] = []
+            }
+          }
+
+          return result
+        }
 
         if (field.localized) {
           result[field.name] = {}

packages/db-postgres/src/transform/write/traverseFields.ts

@@ -335,7 +335,7 @@ export const traverseFields = ({
           })
         }
       } else {
-        if (fieldData === null) {
+        if (fieldData === null || (Array.isArray(fieldData) && fieldData.length === 0)) {
           relationshipsToDelete.push({ path: relationshipPath })
           return
         }

test/relationships/int.spec.ts

@@ -434,6 +434,36 @@ describe('Relationships', () => {
 
         expect(director.docs[0].movies.length).toBeGreaterThan(10)
       })
+
+      it('should allow clearing hasMany relationships', async () => {
+        const fiveMovies = await payload.find({
+          collection: 'movies',
+          limit: 5,
+          depth: 0,
+        })
+
+        const movieIDs = fiveMovies.docs.map((doc) => doc.id)
+
+        const stanley = await payload.create({
+          collection: 'directors',
+          data: {
+            name: 'Stanley Kubrick',
+            movies: movieIDs,
+          },
+        })
+
+        expect(stanley.movies).toHaveLength(5)
+
+        const stanleyNeverMadeMovies = await payload.update({
+          collection: 'directors',
+          id: stanley.id,
+          data: {
+            movies: null,
+          },
+        })
+
+        expect(stanleyNeverMadeMovies.movies).toHaveLength(0)
+      })
     })
   })
 })