Tablestore:Membaca data

Membaca satu baris data

Saat membaca data, Anda dapat menentukan versi data, kolom yang akan dibaca, filter, dan filter ekspresi reguler.

• Membaca versi data terbaru dan kolom tertentu

  Kode contoh berikut menunjukkan cara membaca data versi terbaru dari kolom yang ditentukan pada satu baris dalam tabel data.

  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);
  } 

• Membaca data dengan filter

  Kode contoh berikut menunjukkan cara membaca data versi terbaru dari satu baris dalam tabel data dan menggunakan filter untuk memfilter data berdasarkan nilai kolom Col0.

  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);
  }

• Menggunakan filter ekspresi reguler saat membaca data

  Kode contoh berikut menunjukkan cara membaca data kolom Col1 dari satu baris dalam tabel data dan menggunakan ekspresi reguler untuk memfilter data dalam kolom tersebut.

  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);
  }

Membaca data secara batch

Kode contoh berikut menunjukkan cara mengonfigurasi kondisi versi, kolom yang akan dibaca, dan filter untuk membaca 10 baris 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();
    // The BatchGetRow operation 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. In this example, only the retry request is constructed. 
         * We recommend that you use the custom retry policy in Tablestore SDKs as the retry method. This way, you can retry failed rows after batch operations are performed. After you specify the retry policy, you do not need to add retry code to call the operation. 
         */
        BatchGetRowRequest retryRequest = batchGetRowRequest.createRequestForRetry(batchGetRowResponse.getFailedRows());
    }
}

Membaca data dalam rentang

• Membaca data dalam rentang yang ditentukan

  Kode contoh berikut menunjukkan cara membaca data yang nilai kunci primernya berada dalam rentang yang ditentukan dalam arah maju. Jika nilai parameter nextStartPrimaryKey kosong dalam respons, semua data yang nilai kunci primernya berada dalam rentang yang ditentukan telah dibaca. Jika tidak, Anda harus mengirim permintaan lain hingga semua data yang nilai kunci primernya berada dalam rentang yang ditentukan dikembalikan.

  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;
          }
      }
  }         

• Membaca data berdasarkan rentang yang ditentukan oleh kolom kunci primer pertama

  Kode contoh berikut menunjukkan cara membaca data dalam rentang yang ditentukan oleh nilai kolom kunci primer pertama dalam arah maju. Dalam contoh ini, nilai awal kolom kunci primer kedua diatur ke INF_MIN, dan nilai akhir kolom kunci primer kedua diatur ke INF_MAX. Jika nilai parameter nextStartPrimaryKey null dalam respons, semua data dalam rentang yang ditentukan telah dibaca. Jika tidak, Anda harus mengirim permintaan lain hingga semua data dalam rentang yang ditentukan oleh nilai kolom kunci primer pertama dikembalikan.

  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;
          }
      }
  }    

• Membaca data dalam rentang yang ditentukan dan menerapkan filter ekspresi reguler pada kolom tertentu

  Kode contoh berikut menunjukkan cara membaca data yang nilai kunci primernya berada dalam rentang ["pk:2020-01-01.log", "pk:2021-01-01.log") dari kolom Col1 dan menggunakan ekspresi reguler untuk memfilter data dalam kolom Col1.

  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, 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;
          }
     }
  }