Trying to select data with multiple parameters from DynamoDB

Question

Hi, I have just started working on Dynamodb, i want to create a page on the basis of category, sub category and name using dynamodb and nodeJs However not able to do.  
  
MYSQL Query: Select * from test Where category="1" and sub_category="2" and name="user";  
  
however i don't know how to create this query on dynamodb, whenever I tried to define 2 primary key it return me an error so i have created local secondary key for same below is the **table structure**.  
  
var params = {  
    TableName : "test",  
    KeySchema: \[         
        { AttributeName: "name", KeyType: "HASH"},  //Partition key  
        { AttributeName: "sub_category", KeyType: "RANGE"}  //Sort key  
    ],  
    AttributeDefinitions: \[         
        { AttributeName: "name", AttributeType: "S" },  
        { AttributeName: "sub_category", AttributeType: "S" },  
        { AttributeName: "category", AttributeType: "S" },  
    ],  
    ProvisionedThroughput: {         
        ReadCapacityUnits: 10,   
        WriteCapacityUnits: 10  
    },  
    LocalSecondaryIndexes: \[ // optional (list of LocalSecondaryIndex)  
        {   
            IndexName: 'name_category',  
            KeySchema: \[   
                { // Required HASH type attribute - must match the table's HASH key attribute name  
                    AttributeName: 'name',  
                    KeyType: 'HASH',  
                },  
                { // alternate RANGE key attribute for the secondary index  
                    AttributeName: 'category',   
                    KeyType: 'RANGE',   
                }  
            ],  
            Projection: { // required  
                ProjectionType: 'ALL', // (ALL | KEYS_ONLY | INCLUDE)  
            },  
        },  
        // ... more local secondary indexes ...  
    ],  
};  
  
**DynamoDB Query:**  
  
Curriculum.findtest = function(\[category, sub_category, name], callback){  
     var params = {  
                TableName: "test",  
                IndexNames: "name_category",  
                KeyConditionExpression:"#name= :name and #sub_category = :sub_category and #category = :category",  
                ExpressionAttributeNames:{  
                    "#category": "category",  
                    "#sub_category ": "sub_category",  
                    "#name": "name"  
                },  
                ExpressionAttributeValues: {  
                    ":category": category,  
                    ":sub_category": sub_category,  
                    ":name": name  
                }  
                  
            };  
  
     docClient.query(params, function(err, data) {    
            
        if (err) {  
            console.error("Unable to read item. Error JSON:", JSON.stringify(err, null, 2));    
        } else {  
            callback(null, data.Items);  
            return true;  
     }  
       
    });  
}  
  
**However getting an error in console :**  
  
**Unable to read item. Error JSON: {**  
  **"message": "Conditions can be of length 1 or 2 only",**  
  **"code": "ValidationException",**  
  **"time": "2019-01-18T06:17:04.470Z",**  
  **"requestId": "78406675-5485-4610-bb59-1ddc7976ab17",**  
  **"statusCode": 400,**  
  **"retryable": false,**  
  **"retryDelay": 32.41354621763527**  
**}**  
  
I don't know what am i doing wrong. Kindly assist me.  
  
Thanks in advance.  
  
Edited by: DynamoDev on Jan 18, 2019 12:58 AM

Answer

You can use KeyConditionExpression parameter to provide a specific value for the partition key. You can optionally narrow the scope of the Query operation by specifying a sort key value and a comparison operator in KeyConditionExpression. ( scenario when you have both partition key as well as sort key)  
  
Now, reason you are facing error 'Conditions can be of length 1 or 2 only' is because you are specifying 3 conditions within KeyConditionExpression. Please specify only partition key and sort key. In order to further refine your Query you can optionally provide a FilterExpression on other attributes. A FilterExpression determines which items within the results should be returned to you. All of the other results are discarded.  
  
You can read more about same here: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html  
  
Lastly, you dont need to create a LSI for this purpose. You can perform same operation on original table  
  
Hope this helps

Trying to select data with multiple parameters from DynamoDB

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