Queries items with list attribute type

[nnnvinh]

Amplify Gen 2

Description

When I run queries like :

await client.models.Posts.list({
     filter : {
       post_tags : { contains : 't' }
     }
});

or

await client.models.Posts.list({
     filter : {
       post_tags : { beginsWith : 't' }
     }
});

It return empty data

{
  "data": {
    "listPosts": {
      "items": []
    }
  }
}

But when i run queries with exactly values in list attribute it return expected result

await client.models.Posts.list({
      filter : {
        post_tags : {contains : 'tag1'}
      }
});

returned data

{
  "data": {
    "listPosts": {
      "items": [
        {
          "post_id": "1"
        }
      ]
    }
  }
}

does it normal or a bug?

Database schema

 Posts : a.model({
   post_id : a.string().required(),
   post : a.string(),
   post_tags : a.string().array()
 }).identifier(['post_id'])

Example data to input

{
   post_id : "1",
   post : "post_exmaple",
   post_tags : ["tag1","tag2","tag3"]
}

[pahud]

Current vs Expected Behavior

Current Behavior

// ✅ WORKS: Exact match
filter: { post_tags: { contains: 'tag1' } }
// Returns posts where post_tags array contains exactly 'tag1'

// ❌ FAILS: Partial match  
filter: { post_tags: { contains: 't' } }
// Returns empty results instead of posts with tags containing 't'

// ❌ FAILS: Prefix match
filter: { post_tags: { beginsWith: 't' } }
// Returns empty results instead of posts with tags starting with 't'

Expected Behavior

// Should work: Partial string matching within array elements
filter: { post_tags: { contains: 't' } }
// Expected: Returns posts where any tag contains 't' (tag1, tag2, tag3)

filter: { post_tags: { beginsWith: 't' } }
// Expected: Returns posts where any tag begins with 't' (tag1, tag2, tag3)

---

Hi @nnnvinh

Thank you for reporting this issue. After investigating the behavior you've described, this appears to be a fundamental limitation of how DynamoDB handles filtering operations on string arrays rather than a bug in Amplify.

Current Behavior Explanation:
DynamoDB's contains operation on arrays performs exact element matching, not substring matching within elements. When you filter with { post_tags: { contains: 't' } }, DynamoDB looks for an array element that exactly equals 't', not elements that contain the substring 't'.

Recommended Solutions:

1. For exact tag matching: Continue using the current approach

   filter: { post_tags: { contains: 'tag1' } } // ✅ Works

2. For partial/fuzzy text search: Use the @searchable directive to enable OpenSearch integration:

   const schema = a.schema({
     Posts: a.model({
       post_tags: a.string().array(),
     }).authorization(allow => [allow.publicApiKey()]).searchable(),
   });

3. For custom filtering logic: Implement a custom resolver using the util.transform.toDynamoDBFilterExpression function with additional VTL logic.

Documentation Enhancement:
We should improve our documentation to clarify these array filtering limitations. Would you be interested in contributing to this effort? Community contributions are always welcome!

Related Issues:
This behavior is consistent across multiple Amplify versions and represents the underlying DynamoDB capabilities rather than an Amplify-specific limitation.

Let me know if you'd like guidance on implementing any of these alternative approaches!