fix: filtering by non-poly relationships with not_equals operator (#7573)

## Description

Fixes #5212

Fixes #6278 

- [x] I have read and understand the
[CONTRIBUTING.md](https://github.com/payloadcms/payload/blob/main/CONTRIBUTING.md)
document in this repository.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## Checklist:

- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] Existing test suite passes locally with my changes

test/fields/collections/Relationship/index.ts

@@ -31,6 +31,18 @@ const RelationshipFields: CollectionConfig = {
         },
       },
     },
+    {
+      name: 'relationNoHasManyNonPolymorphic',
+      relationTo: 'text-fields',
+      type: 'relationship',
+      hasMany: false,
+    },
+    {
+      name: 'relationHasManyNonPolymorphic',
+      relationTo: 'text-fields',
+      type: 'relationship',
+      hasMany: true,
+    },
     {
       name: 'relationToSelf',
       relationTo: relationshipFieldsSlug,

test/fields/int.spec.ts

@@ -244,9 +244,6 @@ describe('Fields', () => {
         },
       })
 
-      const anyChildren = await payload.find({
-        collection: relationshipFieldsSlug,
-      })
       const allChildren = await payload.find({
         collection: relationshipFieldsSlug,
         where: {
@@ -1557,7 +1554,47 @@ describe('Fields', () => {
     })
   })
 
-  describe('relationships', () => {
+  describe('relationship queries', () => {
+    let textDoc
+    let otherTextDoc
+    let relationshipDocWithNonPolyOne
+    let relationshipDocWithNonPolyTwo
+    const textDocText = 'text document'
+    const otherTextDocText = 'alt text'
+
+    beforeEach(async () => {
+      textDoc = await payload.create({
+        collection: 'text-fields',
+        data: {
+          text: textDocText,
+        },
+      })
+      otherTextDoc = await payload.create({
+        collection: 'text-fields',
+        data: {
+          text: otherTextDocText,
+        },
+      })
+      const relationship = { relationTo: 'text-fields', value: textDoc.id }
+      relationshipDocWithNonPolyOne = await payload.create({
+        collection: relationshipFieldsSlug,
+        data: {
+          relationship,
+          relationNoHasManyNonPolymorphic: textDoc.id,
+          relationHasManyNonPolymorphic: textDoc.id,
+        },
+      })
+
+      relationshipDocWithNonPolyTwo = await payload.create({
+        collection: relationshipFieldsSlug,
+        data: {
+          relationship,
+          relationNoHasManyNonPolymorphic: otherTextDoc.id,
+          relationHasManyNonPolymorphic: otherTextDoc.id,
+        },
+      })
+    })
+
     it('should not crash if querying with empty in operator', async () => {
       const query = await payload.find({
         collection: 'relationship-fields',
@@ -1570,6 +1607,25 @@ describe('Fields', () => {
 
       expect(query.docs).toBeDefined()
     })
+
+    it('should properly query non-polymorphic relationship with not equals', async () => {
+      const withoutHasMany = await payload.find({
+        collection: relationshipFieldsSlug,
+        where: {
+          relationNoHasManyNonPolymorphic: { not_equals: otherTextDoc.id },
+        },
+      })
+
+      const withHasMany = await payload.find({
+        collection: relationshipFieldsSlug,
+        where: {
+          relationHasManyNonPolymorphic: { not_equals: textDoc.id },
+        },
+      })
+
+      expect(withoutHasMany.docs).toHaveLength(1)
+      expect(withHasMany.docs).toHaveLength(1)
+    })
   })
 
   describe('clearable fields - exists', () => {

test/fields/payload-types.ts

@@ -955,6 +955,8 @@ export interface RelationshipField {
           }
       )[]
     | null
+  relationNoHasManyNonPolymorphic?: (string | null) | TextField
+  relationHasManyNonPolymorphic?: (string | TextField)[] | null
   relationToSelf?: (string | null) | RelationshipField
   relationToSelfSelectOnly?: (string | null) | RelationshipField
   relationWithDynamicDefault?: (string | null) | User