sqlite查询没有执行反应原生

Question

我需要从表格中获取数据＆＃39; pet＆＃39;。 数据库和表是现有的。执行此代码时，将this.state.petname作为＆＃39; def＆＃39;。

var SQLite = require('react-native-sqlite-storage')
var db = SQLite.openDatabase({name:'test.db',createFromLocation:'~sample.db'})
class Register extends Component {

  constructor(props){
    super(props);
    this.state={
      petname: "abc",
    };
    db.transaction((tx) => {
                  this.setState({petname:"def"});

        tx.executeSql('SELECT petname FROM pet WHERE owner = ?',['Mary'],(tx, results) => {
        this.setState({petname:"klm"});
        var len = results.rows.length;
        if(len > 0){
          var row = results.rows.item(0);
          this.setState({petname:row.petname});
        }
        else{
            this.setState({petname:"hij"});
         }

      });
    });
  }
  ............
        }