Tablestore:Read data

Prerequisites

• The OTSClient instance is initialized. For more information, see Initialization.
• A data table is created. Data is written to the table.

Read a single row of data

You can call the GetRow operation to read a single row of data.

API operations

/*
 * Read a single row of data based on a specified primary key. 
 */
getRow(params, callback)
                    

Parameters

Examples

The following code provides an example on how to read a row of data:

var TableStore = require('../index.js');
var Long = TableStore.Long;
var client = require('./client');

var params = {
  tableName: "sampleTable",
  primaryKey: [{ 'gid': Long.fromNumber(20004) }, { 'uid': Long.fromNumber(20004) }],
  maxVersions: 2 // Specify the maximum number of versions that can be read. A value of 2 indicates that you can read a maximum of two versions of data. 
};
var condition = new TableStore.CompositeCondition(TableStore.LogicalOperator.AND);
condition.addSubCondition(new TableStore.SingleColumnCondition('name', 'john', TableStore.ComparatorType.EQUAL));
condition.addSubCondition(new TableStore.SingleColumnCondition('addr', 'china', TableStore.ComparatorType.EQUAL));

params.columnFilter = condition;

client.getRow(params, function (err, data) {
  if (err) {
    console.log('error:', err);
    return;
  }
  console.log('success:', data);
});
                    

To view the detailed sample code, visit GetRow@GitHub.

Read multiple rows of data in a batch

You can call the BatchGetRow operation to read multiple rows of data from one or more tables in a batch. The BatchGetRow operation consists of multiple GetRow operations. The process of constructing a suboperation is the same as the process of calling the GetRow operation. BatchGetRow supports filters.

Note that the BatchGetRow operation uses the same parameter configurations for all rows. For example, if ColumnsToGet is set to [colA], only the value of the colA column is read from all rows.

If you call the BatchGetRow operation, each GetRow operation is separately performed and the response to each GetRow operation is separately returned.

Usage notes

When you call the BatchGetRow operation to read multiple rows in a batch, some rows may fail to be read. If this happens, Tablestore does not return exceptions, but returns BatchGetRowResponse in which the indexes and error messages of the failed rows are included. Therefore, when you call the BatchGetRow operation, you must check the return values to determine whether the status of each row is successful.

Operations

/**
 * Read multiple rows of data from one or more tables. 
 */
batchGetRow(params, callback)                   

Parameters

Example

The following code provides an example on how to read data from multiples tables in a batch and retry the read operations if an error occurs:

var client = require('./client');
var TableStore = require('../index.js');
var Long = TableStore.Long;

var params = {
    tables: [{
        tableName: 'sampleTable',
        primaryKey: [
            [{ 'gid': Long.fromNumber(20013) }, { 'uid': Long.fromNumber(20013) }],
            [{ 'gid': Long.fromNumber(20015) }, { 'uid': Long.fromNumber(20015) }]
        ],
        startColumn: "col2",
        endColumn: "col4"
    },
    {
        tableName: 'notExistTable',
        primaryKey: [
            [{ 'gid': Long.fromNumber(10001) }, { 'uid': Long.fromNumber(10001) }]
        ]
    }
    ],
};

var maxRetryTimes = 3;
var retryCount = 0;

function batchGetRow(params) {
    client.batchGetRow(params, function (err, data) {
        if (err) {
            console.log('error:', err);
            return;
        }

        var isAllSuccess = true;
        var retryRequest = { tables: [] };
        for (var i = 0; i < data.tables.length; i++) {
            var failedRequest = { tableName: data.tables[i][0].tableName, primaryKey: [] };

            for (var j = 0; j < data.tables[i].length; j++) {
                if (!data.tables[i][j].isOk && null != data.tables[i][j].primaryKey) {
                    isAllSuccess = false;
                    var pks = [];
                    for (var k in data.tables[i][j].primaryKey) {
                        var name = data.tables[i][j].primaryKey[k].name;
                        var value = data.tables[i][j].primaryKey[k].value;
                        var kp = {};
                        kp[name] = value;
                        pks.push(kp);
                    }
                    failedRequest.primaryKey.push(pks);

                } else {
                    // get success data
                }
            }

            if (failedRequest.primaryKey.length > 0) {
                retryRequest.tables.push(failedRequest);
            }
        }

        if (!isAllSuccess && retryCount++ < maxRetryTimes) {
            batchGetRow(retryRequest);
        }

        console.log('success:', data);
    });
}

batchGetRow(params, maxRetryTimes);                    

For the detailed sample code, visit BatchGetRow@GitHub.

Read data whose primary key is in a specified range

You can call the GetRange operation to read data whose primary key is in a specified range.

The GetRange operation allows you to read data whose primary key is in a specified range in a forward or backward direction. You can also specify the number of rows to read. If the range is large and the number of scanned rows or the volume of scanned data exceeds the upper limit, the scan stops, and the rows that are read and information about the primary key of the next row are returned. You can initiate a request to start from where the last operation left off and read the remaining rows based on information about the primary key of the next row returned by the previous operation.

Usage notes

GetRange follows the leftmost matching principle. Tablestore compares values in sequence from the first primary key column to the last primary key column to read data whose primary key is in a specified range. For example, the primary key of a data table consists of the following primary key columns: PK1, PK2, and PK3. When data is read, Tablestore first determines whether the PK1 value of a row is in the range that is specified for the first primary key column. If the PK1 value of a row is in the range, Tablestore stops determining whether the values of other primary key columns of the row are in the ranges that are specified for each primary key column and returns the row. If the PK1 value of a row is not in the range, Tablestore continues to determine whether the values of other primary key columns of the row are in the ranges that are specified for each primary key column in the same manner as PK1.

API operations

/**
 * Read data whose primary key is in the specified range. 
 */
getRange(params, callback)                   

Parameters

Examples

The following code provides an example on how to read data whose primary key is in a specified range:

var Long = TableStore.Long;
var client = require('./client');

var params = {
  tableName: "sampleTable",
  direction: TableStore.Direction.FORWARD,
  inclusiveStartPrimaryKey: [{ "gid": TableStore.INF_MIN }, { "uid": TableStore.INF_MIN }],
  exclusiveEndPrimaryKey: [{ "gid": TableStore.INF_MAX }, { "uid": TableStore.INF_MAX }],
  limit: 50
};

client.getRange(params, function (err, data) {
  if (err) {
    console.log('error:', err);
    return;
  }

  // If the value of data.next_start_primary_key is not empty, the system continues to read data. 
  if (data.next_start_primary_key) {

  }

  console.log('success:', data);
});                    

To view the detailed sample code, visit GetRange@GitHub.