如何使WebSQL查询同步？ [英] How to make a WebSQL query synchronous?

问题描述

考虑：

var globalvar;

function viewyearmain() {
  db.transaction(function (tx) 
  {
    tx.executeSql('SELECT * FROM BUDGET WHERE holdingtype="month"', [], function (tx, results) 
    {
       var len = results.rows.length;
       msg = len;
       globalvar = msg;
    }, null);

  });

  if (globalvar>0)
  {
    alert("ROWS FOUND");
  }
  else
  {
    alert("ROWS NOT FOUND");
  }
}

问题在于 ROWS未找到，因为到达 if 语句时交易尚未完成。

The problem is that ROWS NOT FOUND appears because the transaction has not completed by the time the if statement is reached.

推荐答案

异步回调不是同步的，无论你想要它多少。

An asynchronous callback is not synchronous, regardless of how much you want it to be.

只需移动所有代码取决于回调的结果：

Just move all the code the depends on the result into the callback:

var globalvar;

function viewyearmain() {
  db.transaction(function (tx) 
  {
    tx.executeSql('SELECT * FROM BUDGET WHERE holdingtype="month"', [], function (tx, results) 
    {
       var len = results.rows.length;
       msg = len;
       globalvar = msg;
       if (globalvar>0)
       {
         alert("ROWS FOUND");
       }
       else
       {
         alert("ROWS NOT FOUND");
       }
    }, null);

  });
}

或者，将其移至第二个函数，并从回调中调用它。

Alternatively, move it into a second function, and call that from the callback.

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