条件更新

前提条件

初始化Tablestore Client

功能说明

条件更新的类声明如下：

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

示例代码

以下示例代码以 updateRow 方法为例介绍如何设置条件更新。

public static void setConditionExample(SyncClient client) {
    // 构造更新数据
    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"));

    // 构造更新条件
    Condition condition = new Condition();
    // 目标行数据在数据表中存在时才进行数据更新
    condition.setRowExistenceExpectation(RowExistenceExpectation.EXPECT_EXIST);
    rowUpdateChange.setCondition(condition);

    // 构造 Request，调用 updateRow 方法更新数据
    UpdateRowRequest updateRowRequest = new UpdateRowRequest(rowUpdateChange);
    UpdateRowResponse updateRowResponse = client.updateRow(updateRowRequest);

    // 返回结果处理
    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());
}

• 设置列值判断条件，判断单个属性列的值是否满足条件。

  // col1 列的值等于 val1 时才进行数据更新
  SingleColumnValueCondition singleColumnValueCondition = new SingleColumnValueCondition("col1", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val1"));
  condition.setColumnCondition(singleColumnValueCondition);

• 设置列值判断条件，对多个条件进行判断。

  // 设置组合条件 1
  CompositeColumnValueCondition compositeColumnValueCondition1 = new CompositeColumnValueCondition(CompositeColumnValueCondition.LogicOperator.AND);
  // 添加子条件
  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);
  // 设置组合条件 2
  CompositeColumnValueCondition compositeColumnValueCondition2 = new CompositeColumnValueCondition(CompositeColumnValueCondition.LogicOperator.OR);
  // 添加子条件
  compositeColumnValueCondition2.addCondition(compositeColumnValueCondition1);
  SingleColumnValueCondition singleColumnValueCondition3 = new SingleColumnValueCondition("col3", SingleColumnValueCondition.CompareOperator.EQUAL, ColumnValue.fromString("val3"));
  compositeColumnValueCondition2.addCondition(singleColumnValueCondition3);
  // 添加组合条件，判断条件为 (col1 = val1 and col2 = val2) or (col3 = val3)
  condition.setColumnCondition(compositeColumnValueCondition2);

场景案例

以下示例代码使用条件更新功能模拟乐观锁的 CAS 实现。

public static void OptimisticLocking(SyncClient client) {
    // 构造主键
    PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
    primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.fromString("row1"));
    PrimaryKey primaryKey = primaryKeyBuilder.build();

    // 读取原属性列的值
    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();

    // 更新数据
    RowUpdateChange rowUpdateChange = new RowUpdateChange("test_condition", primaryKey);
    rowUpdateChange.put("col1", ColumnValue.fromString("changed_val1"));
    // 设置更新条件，目标属性列最新版本的值等于预期值（读取到的值）时，才进行更新
    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);

    // 构造 Request，调用 updateRow 方法更新数据
    UpdateRowRequest updateRowRequest = new UpdateRowRequest(rowUpdateChange);
    UpdateRowResponse updateRowResponse = client.updateRow(updateRowRequest);

    // 返回结果处理
    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());
}