Tablestore:Use a secondary index to read data

Parameters

When you call the GetRow operation to read data from an index table, take note of the following items:

• You must set the tableName parameter to the name of the index table.

• Tablestore automatically adds the primary key columns of the data table that are not specified as index columns to an index table as the primary key columns of the index table. Therefore, when you specify the primary key columns of a row in an index table, you must specify the index columns based on which you create the index table and the primary key columns of the data table.

Examples

The following sample code provides an example on how to read a row of data in an index table based on the primary key of the row:

public static void GetRowfromIndex()
{
    OTSClient otsClient = Config.GetClient();
    // Construct the primary key. When you construct the primary key, you must specify the primary key columns of the data table that are not specified as index columns. 
    PrimaryKey primaryKey = new PrimaryKey
    {
        { "col0", new ColumnValue(0) },
        { "pk1", new ColumnValue(0) },
        { "pk2", new ColumnValue("abc") }
    };

    try
    {
        // Construct a query request object. The entire row is read if no attribute column is specified. 
        var request = new GetRowRequest(IndexName, primaryKey);

        // Call the GetRow operation to query data. 
        var response = otsClient.GetRow(request);

        Console.WriteLine("Primary Key: " + response.PrimaryKey);
        Console.WriteLine("Attribute Column: " + response.Columns[0]);

        // If no exception is returned, the operation is successful. 
        Console.WriteLine("Get row succeeded.");
    }
    catch (Exception ex)
    {
        // If an exception is returned, the operation fails. Handle the exception. 
        Console.WriteLine("Get row failed, exception:{0}", ex.Message);
    }
}

Parameters

When you call the GetRange operation to read data from an index table, take note of the following items:

• You must set the tableName parameter to the name of the index table.

• Tablestore automatically adds the primary key columns of the data table that are not specified as index columns to an index table as the primary key columns of the index table. Therefore, when you specify the start primary key and end primary key of the range that you want to query, you must specify the index columns based on which you create the index table and the primary key columns of the data table.

Examples

The following sample code provides an example on how to read data whose primary key values are within a specific range from an index table. In this example, the first primary key column of the index table is col1. The value that is specified for the col1 column for the range is 0.

public static void GetRangeFromIndexTable()
{
    Console.WriteLine("Start getRange from index...");
    OTSClient otsClient = Config.GetClient();
    // Specify the value of the first primary key column col1 and scan the data. 
    PrimaryKey inclusiveStartPrimaryKey = new PrimaryKey
    {
        { "col1", new ColumnValue(0) },
        { "pk1",  ColumnValue.INF_MIN },
        { "pk2", ColumnValue.INF_MIN }
    };

    PrimaryKey exclusiveEndPrimaryKey = new PrimaryKey
    {
        { "col1", new ColumnValue(0) },
        { "pk1",  ColumnValue.INF_MAX },
        { "pk2", ColumnValue.INF_MAX }
    };

    GetRangeRequest request = new GetRangeRequest(IndexName, GetRangeDirection.Forward, inclusiveStartPrimaryKey, exclusiveEndPrimaryKey);

    GetRangeResponse response = otsClient.GetRange(request);
    IList<Row> rows = response.RowDataList;
    PrimaryKey nextStartPrimaryKey = response.NextPrimaryKey;
    while (nextStartPrimaryKey != null)
    {
        request = new GetRangeRequest(TableName, GetRangeDirection.Forward, nextStartPrimaryKey, exclusiveEndPrimaryKey);
        response = otsClient.GetRange(request);
        nextStartPrimaryKey = response.NextPrimaryKey;
        foreach (var row in response.RowDataList)
        {
            rows.Add(row);
        }
    }

    foreach (var row in rows)
    {
        PrintRow(row);
    }

    Console.WriteLine("TotalRowsRead: " + rows.Count);
}

private static void PrintRow(Row row)
{
    Console.WriteLine("-----------------");

    foreach (KeyValuePair<string, ColumnValue> entry in row.GetPrimaryKey())
    {
        Console.WriteLine(entry.Key + ":" + entry.Value);
    }

    foreach (Column entry in row.GetColumns())
    {
        Console.WriteLine(entry.Name + ":" + entry.Value);
    }

    Console.WriteLine("-----------------");
}