Query NoSQL Table

Catalyst enables you to query a NoSQL table and retrieve data by identifying the items using the primary keys of the table. For instance, you can use just the partition key or a combination of the partition key and sort key to retrieve the item.

You can define the key condition that identifies the item by specifying the attributes, their required values, and the supported operator to be used. The supported operators are represented as shown below.

In the example below, the query is executed using the queryTable() method by identifying the items using the partition key fruitType and specifying the condition value as “Citrus”.

Catalyst NoSQL also lets you define other elements of the query, such as using consistent_read to indicate if the read operation must be done using the master or a slave cluster, limiting the number of rows to be returned, and specifying the sorting order as ascending.

The no-sql library from the zcatalyst-sdk-node package is required to define the NoSQL item.

    

        
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         const { NoSQLMarshall, NoSQLEnum } = require('zcatalyst-sdk-node/lib/no-sql');
const { NoSQLOperator } = NoSQLEnum;

// Query a NoSQL table to fetch the items identified by the partition key fruitType with the value "citrus"
const queriedItem = await table.queryTable({
 // Define the key condition to query the items with
 key_condition: {
  // Specify the partition key attribute name of the table
  attribute: 'fruitType',
  // Define the supported operator to be used. You can also use BETWEEN, GREATERTHAN, LESSERTHAN, GREATERTHANOREQUALTO, LESSERTHANOREQUALTO
  operator: NoSQLOperator.EQUALS,
  // Specify the value for comparison
  value: NoSQLMarshall.makeString('Citrus')
 },
 // Set consistent_read to true to query from master. If set to false, it is queried from slave.
 consistent_read: true,
 // Limit the number of rows to be returned by specifying a value
 limit: 10,
 // Set forward_scan to true to sort the results in ascending order. Otherwise, it is sorted in the descending order.
 forward_scan: true
});