Tablestore:Read data

Read a single row of data

You can specify the data version and the columns that you want to read, and filter the data by using a filter or a regular expression.

• Read data of the latest version from the specified columns of a row

  The following sample code provides an example on how to read data of the latest version from the specified columns of a row in a data table.

  private static void getRow(SyncClient client, String pkValue) {
      // Construct the primary key. 
      PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString(pkValue));
      PrimaryKey primaryKey = primaryKeyBuilder.build();
  
      // Specify the table name and primary key to read a row of data. 
      SingleRowQueryCriteria criteria = new SingleRowQueryCriteria("<TABLE_NAME>", primaryKey);
      // Set the MaxVersions parameter to 1 to read the latest version of data. 
      criteria.setMaxVersions(1);
      GetRowResponse getRowResponse = client.getRow(new GetRowRequest(criteria));
      Row row = getRowResponse.getRow();
  
      System.out.println("Read complete. Result:");
      System.out.println(row);
  
      // Specify the columns that you want to read. 
      criteria.addColumnsToGet("Col0");
      getRowResponse = client.getRow(new GetRowRequest(criteria));
      row = getRowResponse.getRow();
  
      System.out.println("Read complete. Result:");
      System.out.println(row);
  } 

• Use a filter to filter data that is read

  The following sample code provides an example on how to read data of the latest version from a row in a data table and use a filter to filter data based on the value of the Col0 column.

  private static void getRow(SyncClient client, String pkValue) {
      // Construct the primary key. 
      PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString(pkValue));
      PrimaryKey primaryKey = primaryKeyBuilder.build();
  
      // Specify the table name and primary key to read a row of data. 
      SingleRowQueryCriteria criteria = new SingleRowQueryCriteria("<TABLE_NAME>", primaryKey);
      // Set the MaxVersions parameter to 1 to read the latest version of data. 
      criteria.setMaxVersions(1);
  
      // Configure a filter to return a row in which the value of the Col0 column is 0. 
      SingleColumnValueFilter singleColumnValueFilter = new SingleColumnValueFilter("Col0",
              SingleColumnValueFilter.CompareOperator.EQUAL, ColumnValue.fromLong(0));
      // If the Col0 column does not exist, the row is not returned. 
      singleColumnValueFilter.setPassIfMissing(false);
      criteria.setFilter(singleColumnValueFilter);
  
      GetRowResponse getRowResponse = client.getRow(new GetRowRequest(criteria));
      Row row = getRowResponse.getRow();
  
      System.out.println("Read complete. Result:");
      System.out.println(row);
  }

• Use a regular expression to filter data that is read

  The following sample code provides an example on how to read the data of the Col1 column from a row in a data table and use a regular expression to filter data in the column.

  private static void getRow(SyncClient client, String pkValue) {
      // Specify the name of the data table. 
      SingleRowQueryCriteria criteria = new SingleRowQueryCriteria("<TABLE_NAME>");
   
      // Construct the primary key. 
      PrimaryKey primaryKey = PrimaryKeyBuilder.createPrimaryKeyBuilder()
          .addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString(pkValue))
          .build();
      criteria.setPrimaryKey(primaryKey);
   
      // Set the MaxVersions parameter to 1 to read the latest version of data. 
      criteria.setMaxVersions(1);
   
      // Configure a filter. A row is returned when cast<int>(regex(Col1)) is greater than 100. 
      RegexRule regexRule = new RegexRule("t1:([0-9]+),", RegexRule.CastType.VT_INTEGER);
      SingleColumnValueRegexFilter filter =  new SingleColumnValueRegexFilter("Col1",
          regexRule,SingleColumnValueRegexFilter.CompareOperator.GREATER_THAN, ColumnValue.fromLong(100));
      criteria.setFilter(filter);
   
      GetRowResponse getRowResponse = client.getRow(new GetRowRequest(criteria));
      Row row = getRowResponse.getRow();
  
      System.out.println("Read complete. Result:");
      System.out.println(row);
  }

Read multiple rows of data at a time

The following sample code provides an example on how to configure the version conditions, columns to read, and filters to read 10 rows of data.

private static void batchGetRow(SyncClient client) {
    // Specify the name of the data table. 
    MultiRowQueryCriteria multiRowQueryCriteria = new MultiRowQueryCriteria("<TABLE_NAME>");
    // Specify 10 rows that you want to read. 
    for (int i = 0; i < 10; i++) {
        PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
        primaryKeyBuilder.addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString("pk" + i));
        PrimaryKey primaryKey = primaryKeyBuilder.build();
        multiRowQueryCriteria.addRow(primaryKey);
    }
    // Add conditions. 
    multiRowQueryCriteria.setMaxVersions(1);
    multiRowQueryCriteria.addColumnsToGet("Col0");
    multiRowQueryCriteria.addColumnsToGet("Col1");
    SingleColumnValueFilter singleColumnValueFilter = new SingleColumnValueFilter("Col0",
            SingleColumnValueFilter.CompareOperator.EQUAL, ColumnValue.fromLong(0));
    singleColumnValueFilter.setPassIfMissing(false);
    multiRowQueryCriteria.setFilter(singleColumnValueFilter);

    BatchGetRowRequest batchGetRowRequest = new BatchGetRowRequest();
    // BatchGetRow allows you to read data from multiple tables. Each multiRowQueryCriteria parameter specifies query conditions for one table. You can add multiple multiRowQueryCriteria parameters to read data from multiple tables. 
    batchGetRowRequest.addMultiRowQueryCriteria(multiRowQueryCriteria);

    BatchGetRowResponse batchGetRowResponse = client.batchGetRow(batchGetRowRequest);

    System.out.println("Whether all operations are successful:" + batchGetRowResponse.isAllSucceed());
    System.out.println("Read complete. Result:");
    for (BatchGetRowResponse.RowResult rowResult : batchGetRowResponse.getSucceedRows()) {
        System.out.println(rowResult.getRow());
    }
    if (!batchGetRowResponse.isAllSucceed()) {
        for (BatchGetRowResponse.RowResult rowResult : batchGetRowResponse.getFailedRows()) {
            System.out.println("Failed rows:" + batchGetRowRequest.getPrimaryKey(rowResult.getTableName(), rowResult.getIndex()));
            System.out.println("Cause of failures:" + rowResult.getError());
        }

        /**
         * You can use the createRequestForRetry method to construct another request to retry the operations on failed rows. Only the retry request is constructed here. 
         * We recommend that you use the custom retry policy in Tablestore SDKs as the retry method. This feature allows you to retry failed rows after batch operations. After you set the retry policy, you do not need to add retry code to call the operation. 
         */
        BatchGetRowRequest retryRequest = batchGetRowRequest.createRequestForRetry(batchGetRowResponse.getFailedRows());
    }
}

Read data whose primary key values are in the specified range

• Read data whose primary key values are in the specified range

  The following sample code provides an example on how to read data whose primary key values are in the specified range in the forward direction. If the value of the nextStartPrimaryKey parameter is empty in the response, all data whose primary key values are in the specified range is read.

  private static void getRange(SyncClient client, String startPkValue, String endPkValue) {
      // Specify the name of the data table. 
      RangeRowQueryCriteria rangeRowQueryCriteria = new RangeRowQueryCriteria("<TABLE_NAME>");
  
      // Specify the start primary key. 
      PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString(startPkValue));
      rangeRowQueryCriteria.setInclusiveStartPrimaryKey(primaryKeyBuilder.build());
  
      // Specify the end primary key. 
      primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString(endPkValue));
      rangeRowQueryCriteria.setExclusiveEndPrimaryKey(primaryKeyBuilder.build());
  
      rangeRowQueryCriteria.setMaxVersions(1);
  
      System.out.println("GetRange result:");
      while (true) {
          GetRangeResponse getRangeResponse = client.getRange(new GetRangeRequest(rangeRowQueryCriteria));
          for (Row row : getRangeResponse.getRows()) {
              System.out.println(row);
          }
  
          // If the value of the nextStartPrimaryKey parameter is not null, continue the read operation. 
          if (getRangeResponse.getNextStartPrimaryKey() != null) {
              rangeRowQueryCriteria.setInclusiveStartPrimaryKey(getRangeResponse.getNextStartPrimaryKey());
          } else {
              break;
          }
      }
  }         

• Read data within the range determined by the value of the first primary key column

  The following sample code provides an example on how to read data in the forward direction within the range determined by the value of the first primary key column. The start value of the second primary key column is of the INF_MIN type. The end value of the second primary key column is of the INF_MAX type. If the value of the nextStartPrimaryKey parameter is null in the response, all data in the specified range is read.

  private static void getRange(SyncClient client, String startPkValue, String endPkValue) {
      // Specify the name of the data table. 
      RangeRowQueryCriteria rangeRowQueryCriteria = new RangeRowQueryCriteria("<TABLE_NAME>");
      // Specify the start primary key. In this example, two primary key columns are used. 
      PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk1", PrimaryKeyValue.fromString(startPkValue));// Set the value of the first primary key column to a specific value. 
      primaryKeyBuilder.addPrimaryKeyColumn("pk2", PrimaryKeyValue.INF_MIN);// Set the value of the second primary key column to an infinitely small value. 
      rangeRowQueryCriteria.setInclusiveStartPrimaryKey(primaryKeyBuilder.build());
  
      // Specify the end primary key. 
      primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
      primaryKeyBuilder.addPrimaryKeyColumn("pk1", PrimaryKeyValue.fromString(endPkValue));// Set the value of the first primary key column to a specific value. 
      primaryKeyBuilder.addPrimaryKeyColumn("pk2", PrimaryKeyValue.INF_MAX);// Set the value of the second primary key column to an infinitely great value. 
      rangeRowQueryCriteria.setExclusiveEndPrimaryKey(primaryKeyBuilder.build());
  
      rangeRowQueryCriteria.setMaxVersions(1);
  
      System.out.println("GetRange result:");
      while (true) {
          GetRangeResponse getRangeResponse = client.getRange(new GetRangeRequest(rangeRowQueryCriteria));
          for (Row row : getRangeResponse.getRows()) {
              System.out.println(row);
          }
  
          // If the value of the nextStartPrimaryKey parameter is not null, continue the read operation. 
          if (getRangeResponse.getNextStartPrimaryKey() != null) {
              rangeRowQueryCriteria.setInclusiveStartPrimaryKey(getRangeResponse.getNextStartPrimaryKey());
          } else {
              break;
          }
      }
  }    

• Read data whose primary key values are in the specified range and use a regular expression to filter data in the specified column

  The following sample code provides an example on how to read data whose primary key values are in the range of ["pk:2020-01-01.log", "pk:2021-01-01.log") from the Col1 column and use a regular expression to filter data in the Col1 column.

  private static void getRange(SyncClient client) {
      // Specify the name of the data table. 
      RangeRowQueryCriteria criteria = new RangeRowQueryCriteria("<TABLE_NAME>");
   
      // Specify ["pk:2020-01-01.log", "pk:2021-01-01.log") as the range of the primary key of the data that you want to read. The range is a left-closed and right-open interval. 
      PrimaryKey pk0 = PrimaryKeyBuilder.createPrimaryKeyBuilder()
          .addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString("2020-01-01.log"))
          .build();
      PrimaryKey pk1 = PrimaryKeyBuilder.createPrimaryKeyBuilder()
          .addPrimaryKeyColumn("pk", PrimaryKeyValue.fromString("2021-01-01.log"))
          .build();
      criteria.setInclusiveStartPrimaryKey(pk0);
      criteria.setExclusiveEndPrimaryKey(pk1);
   
      // Set the MaxVersions parameter to 1 to read the latest version of data. 
      criteria.setMaxVersions(1);
   
      // Configure a filter. A row is returned when cast<int>(regex(Col1)) is greater than 100. 
      RegexRule regexRule = new RegexRule("t1:([0-9]+),", RegexRule.CastType.VT_INTEGER);
      SingleColumnValueRegexFilter filter =  new SingleColumnValueRegexFilter("Col1",
          regexRule,SingleColumnValueRegexFilter.CompareOperator.GREATER_THAN,ColumnValue.fromLong(100));
      criteria.setFilter(filter);
  
      while (true) {
          GetRangeResponse resp = client.getRange(new GetRangeRequest(criteria));
          for (Row row : resp.getRows()) {
              // do something
              System.out.println(row);
          }
          if (resp.getNextStartPrimaryKey() != null) {
              criteria.setInclusiveStartPrimaryKey(resp.getNextStartPrimaryKey());
          } else {
              break;
          }
     }
  }