Tablestore:Atualização condicional

Pré-requisitos

Inicializar um cliente

Descrição

A classe Condition é declarada da seguinte forma:

public class Condition {
    private RowExistenceExpectation rowExistenceExpectation;
    private ColumnCondition columnCondition;
    
    // Method declaration
}

Código de exemplo

O exemplo de código a seguir mostra como realizar uma atualização condicional usando o método updateRow.

public static void setConditionExample(SyncClient client) {
    // Construct the update data.
    PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
    primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.fromString("row1"));
    PrimaryKey primaryKey = primaryKeyBuilder.build();
    RowUpdateChange rowUpdateChange = new RowUpdateChange("test_condition", primaryKey);
    rowUpdateChange.put("col1", ColumnValue.fromString("changed_val1"));

    // Construct the update condition.
    Condition condition = new Condition();
    // Update the data only if the target row exists in the data table.
    condition.setRowExistenceExpectation(RowExistenceExpectation.EXPECT_EXIST);
    rowUpdateChange.setCondition(condition);

    // Construct a request and call the updateRow method to update the data.
    UpdateRowRequest updateRowRequest = new UpdateRowRequest(rowUpdateChange);
    UpdateRowResponse updateRowResponse = client.updateRow(updateRowRequest);

    // Process the response.
    System.out.println("* RequestId: " + updateRowResponse.getRequestId());
    System.out.println("* Read CU Cost: " + updateRowResponse.getConsumedCapacity().getCapacityUnit().getReadCapacityUnit());
    System.out.println("* Write CU Cost: " + updateRowResponse.getConsumedCapacity().getCapacityUnit().getWriteCapacityUnit());
}

• Defina uma condição de valor de coluna para verificar se o valor de uma única coluna de atributo atende a uma condição especificada.

  // Update the data only if the value of the col1 column is val1.
  SingleColumnValueCondition singleColumnValueCondition = new SingleColumnValueCondition("col1", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val1"));
  condition.setColumnCondition(singleColumnValueCondition);

• Defina uma condição de valor de coluna para verificar várias subcondições.

  // Set composite condition 1.
  CompositeColumnValueCondition compositeColumnValueCondition1 = new CompositeColumnValueCondition(CompositeColumnValueCondition.LogicOperator.AND);
  // Add sub-conditions.
  SingleColumnValueCondition singleColumnValueCondition1 = new SingleColumnValueCondition("col1", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val1"));
  compositeColumnValueCondition1.addCondition(singleColumnValueCondition1);
  SingleColumnValueCondition singleColumnValueCondition2 = new SingleColumnValueCondition("col2", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val2"));
  compositeColumnValueCondition1.addCondition(singleColumnValueCondition2);
  // Set composite condition 2.
  CompositeColumnValueCondition compositeColumnValueCondition2 = new CompositeColumnValueCondition(CompositeColumnValueCondition.LogicOperator.OR);
  // Add sub-conditions.
  compositeColumnValueCondition2.addCondition(compositeColumnValueCondition1);
  SingleColumnValueCondition singleColumnValueCondition3 = new SingleColumnValueCondition("col3", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val3"));
  compositeColumnValueCondition2.addCondition(singleColumnValueCondition3);
  // Add the composite condition. The condition is (col1 = val1 and col2 = val2) or (col3 = val3).
  condition.setColumnCondition(compositeColumnValueCondition2);

Caso de uso

O exemplo de código a seguir mostra como usar o recurso de atualização condicional para simular uma operação de comparação e troca (CAS) para bloqueio otimista.

public static void OptimisticLocking(SyncClient client) {
    // Construct the primary key.
    PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
    primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.fromString("row1"));
    PrimaryKey primaryKey = primaryKeyBuilder.build();

    // Read the original value of the attribute column.
    SingleRowQueryCriteria singleRowQueryCriteria = new SingleRowQueryCriteria("test_condition", primaryKey);
    singleRowQueryCriteria.setMaxVersions(1);
    GetRowRequest getRowRequest = new GetRowRequest(singleRowQueryCriteria);
    GetRowResponse getRowResponse = client.getRow(getRowRequest);
    String oldValue = getRowResponse.getRow().getLatestColumn("col1").getValue().asString();

    // Update the data.
    RowUpdateChange rowUpdateChange = new RowUpdateChange("test_condition", primaryKey);
    rowUpdateChange.put("col1", ColumnValue.fromString("changed_val1"));
    // Set the update condition. The update is performed only if the latest version of the target attribute column equals the expected value (the read value).
    Condition condition = new Condition(RowExistenceExpectation.EXPECT_EXIST);
    SingleColumnValueCondition singleColumnValueCondition = new SingleColumnValueCondition("col1", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString(oldValue));
    singleColumnValueCondition.setPassIfMissing(false);
    singleColumnValueCondition.setLatestVersionsOnly(true);
    condition.setColumnCondition(singleColumnValueCondition);
    rowUpdateChange.setCondition(condition);

    // Construct a request and call the updateRow method to update the data.
    UpdateRowRequest updateRowRequest = new UpdateRowRequest(rowUpdateChange);
    UpdateRowResponse updateRowResponse = client.updateRow(updateRowRequest);

    // Process the response.
    System.out.println("* RequestId: " + updateRowResponse.getRequestId());
    System.out.println("* Read CU Cost: " + updateRowResponse.getConsumedCapacity().getCapacityUnit().getReadCapacityUnit());
    System.out.println("* Write CU Cost: " + updateRowResponse.getConsumedCapacity().getCapacityUnit().getWriteCapacityUnit());
}