我使用以下代码从 Web SQL 数据库获取分层数据:
...
function getResult(query, data, callback){
db.transaction(function(tx) {
tx.executeSql(query, data, function(tx, result) {
callback(result);
});
});
}
function findChildren(id){
getResult("SELECT * FROM my_table WHERE parent_id=?", [id], function(result){
for (var i = 0, item = null; i < result.rows.length; i++) {
item = result.rows.item(i);
data.push(item);
findChildren(item.id);
}
});
}
var data = Array();
getResult("SELECT * FROM my_table WHERE name like ?", ["A"], function(result){
for (var i = 0, item = null; i < result.rows.length; i++) {
item = result.rows.item(i);
data.push(item);
findChildren(item.id);
}
});
...
如何检测执行是否完成?
使用回调findChildren
以及未平仓交易柜台:
function findChildren(id, callback){
getResult("SELECT * FROM my_table WHERE parent_id=?", [id], function(result){
var results = [],
results.finished = 0;
len = result.rows.length;
for (var i = 0; i < len; i++) (function(i) {
var item = result.rows.item(i);
...
...
findChildren(item.id, function(result) {
results[i] = result;
if (++results.finished == len)
callback(results);
});
})(i);
});
}
getResult("SELECT * FROM my_table WHERE name like ?", ["A"], function(result){
var results = [],
results.finished = 0,
len = result.rows.length;
for (var i = 0; i < len; i++) (function(i) {
var item = result.rows.item(i);
...
...
findChildren(item.id, function(result) {
results[i] = result;
if (++results.finished == len) {
// now results contains a nice tree of arrays with children ids
// do something with it
}
});
})(i);
});
Promise 将抽象计数器并简化回调处理。此外,由于您的两个查询非常相似,您可能也希望将它们抽象为一个通用函数。
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