How to query DynamoDB with non-primary key column

While building my most recent web app, I was deploying the app to AWS and using DynamoDB for storage. DynamoDB is a NoSql database by AWS. I have written about how to CRUD data to it in an earlier post but this post talks about how to query DynamoDB with non-primary key column in the where clause. This post will include code samples along with step-by-step instructions on how to configure AWS DynamoDB admin to enable filtering rows by non-primary key column.

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How to query DynamoDB with non-primary key column Conclusion

How to query DynamoDB with non-primary key column

In this tutorial we will use the table defined in this repo cptdanko/node_typescript_crud_notes (github.com) to create an index. Based on that repository, if you had to create an index for the user_id column for the Todo table, you would follow the steps below,

Open DynamoDB dashboard in AWS console
Click on tables
Open table details in the column
Click on the index tab
From the Actions drop-down click on Create index
Enter the following values in the fields you see
- Partition key: user_id
- Sort key – you can leave it blank
- Index name – user_id-index (it can be anything you want)
Click on the Create index button

Great and having created the index, you can now query the Todo table and filter the values by the user_id column.

In terms of how to retrieve it in your NodeJS code, while the code below is not efficient, it is sufficient to demonstrate the concept talked about in this post.

  /**
   * While the code below works
   * DocumentClient.scan is very ineffecient, as such
   * Improve this as part of another issue
   * @param userId 
   * @returns 
   */
  async getTodoByUser(userId: string): Promise<QueryOutput> {
    const params = {
      TableName: TODO_TABLE,
      FilterExpression: '#userid = :user',
      ExpressionAttributeNames: {
        "#userid": "user_id"
      },
      ExpressionAttributeValues: {
        ':user': userId
      },
    };
    return this.documentClient.scan(params).promise();
  }

That’s it, you can refer to the full code to query DynamoDB in this file here of this repository.

node_typescript_crud_notes/ddbTodo.ts at main · cptdanko/node_typescript_crud_notes (github.com)