如何使用Datastax Java驱动程序以通用方式将值绑定到bound语句? [英] How to bind values to bound statement in a generic way using datastax java driver?

问题描述

我正在使用Datastax Java驱动程序来读写Cassandra中的数据.我正在使用datastax Java驱动程序3.1.0，而我的cassandra群集版本是2.0.10.

I am working with Datastax Java driver to read and write data into Cassandra. I am using datastax java driver 3.1.0 and my cassandra cluster version is 2.0.10.

我创建了以下两种方法来执行cql查询.

I have created below two methods to execute my cql query.

当我不需要在cql查询中设置任何值时，我正在调用第一个方法，因此它适用于cql字符串，如下所示:

I am calling first method when I don't need to set any value in my cql query so it works for cql string like below:

select * from testkeyspace.testtable where row_id=1 // cql-1
select * from testkeyspace.meta where row_id=1 // cql-2
select * from testkeyspace.proc where row_id=1 // cql-3

现在，只要有这样的查询，我就需要调用第二种方法:

Now I need to call second method whenever I have query like this:

select * from testkeyspace.testtabletwo where row_id=1 and active=? // cql-4
select * from testkeyspace.storage where topic=? and parts=? // cql-5, in this part is Integer and topic is String.

所以我的问题是如何使第二种方法更通用，以便如果我需要使用BoundStatement在cql查询中设置n个值，它应该可以工作?现在，我不确定用传递给该方法的值调用第二个方法时应该对cql-4和cql-5做什么?我知道我必须使用BoundStatement设置这些值，但是如果我需要设置两个或三个或四个值，如何使该方法通用，这样我就不需要硬编码了?有些可以是整数，有些可以是字符串.

So my question is how can I make my second method more generic so that if I need to set n number of values in my cql query using BoundStatement, it should work? Right now I am not sure what I am supposed to do for cql-4 and cql-5 while calling my second method with values passed to that method? I know I have to set those values using BoundStatement but if I need to set two or three or four value, how can I make that method generic so that I don't need to hardcode anything? Some can be Integer and some can be String.

第一种方法:-

  public ResultSet executeQuery(final String cql) {
    return executeWithSession(new SessionCallable<ResultSet>() {
      @Override
      public ResultSet executeWithSession(Session session) {
        BoundStatement bs = getStatement(cql);
        bs.setConsistencyLevel(consistencyLevel);
        return session.execute(bs);
      }
    });
  }

第二种方法:-

  public ResultSet executeQuery(final String cql, final Object... values) {
    return executeWithSession(new SessionCallable<ResultSet>() {
      @Override
      public ResultSet executeWithSession(Session session) {
        BoundStatement bs = getStatement(cql);
        bs.setConsistencyLevel(consistencyLevel);
        // how to set these **values** into my cql query using BoundStatement in a generic way 
        // so that I don't need to hardcode anything for cql-4 and cql-5
        return session.execute(cql, values);
      }
    });
  }

  // cache the prepared statement
  private BoundStatement getStatement(final String cql) {
    Session session = getSession();
    PreparedStatement ps = cache.get(cql);
    // no statement cached, create one and cache it now.
    if (ps == null) {
      ps = session.prepare(cql);
      PreparedStatement old = cache.putIfAbsent(cql, ps);
      if (old != null)
        ps = old;
    }
    return ps.bind();
  }

我必须在这里使用BoundStatement吗?我猜我必须这样做，因为那是我可以设置一致性级别的方法?

Do I have to use BoundStatement here at all? I guess I have to because that's how I can set consistency level?

推荐答案

那呢:

public ResultSet executeQuery(final String cql, final Object... values) {
    return executeWithSession(new SessionCallable<ResultSet>() {
        @Override
        public ResultSet executeWithSession(Session session) {
            BoundStatement bs = getStatement(cql, values);
            bs.setConsistencyLevel(consistencyLevel);
            return session.execute(cql);
        }
    });
}

// cache the prepared statement
private BoundStatement getStatement(final String cql, Object... values) {
    Session session = getSession();
    PreparedStatement ps = cache.get(cql);
    // no statement cached, create one and cache it now.
    if (ps == null) {
        ps = session.prepare(cql);
        PreparedStatement old = cache.putIfAbsent(cql, ps);
        if (old != null)
            ps = old;
    }
    return ps.bind(values);
}

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