async.waterfall 从不执行第二个函数
async.waterfall never executes second function
为什么这里的第二个函数永远不会执行:
async.waterfall([
function(waterfallCb) {
console.log("step1");
countDocuments(db,waterfallCb);
}, function(waterfallCb) {
console.log("Step2");
insertDocument(db,waterfallCb);
}], function(err,data){
console.log("in waterfall callback");
db.close();
});
输出:
step1
in waterfall callback
为什么第二个函数(打印步骤 2)从未被调用?
编辑:这是 countDocuments:
var countDocuments = function(db,callback){
var collection = db.collection(colname);
collection.find({}).toArray(function(err,docs){
assert.equal(err, null);
console.log("Found %d records",docs.length);
callback(docs);
});
};
编辑:插入文档:
var insertDocument = function(db, callback){
var collection = db.collection(colname);
collection.insertOne(sampleDoc, function(err,result){
assert.equal(err, null);
assert.equal(1, result.result.n);
assert.equal(1, result.ops.length);
console.log("inserted 1 document into the collection");
callback(null, 'one');
});
};
由于您使用 caolan/async
,第一个参数是错误对象,在您的情况下,如果它不是空值,则可能会告诉 async 您有错误并且不再继续。这是文档中的示例:
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
});
为什么这里的第二个函数永远不会执行:
async.waterfall([
function(waterfallCb) {
console.log("step1");
countDocuments(db,waterfallCb);
}, function(waterfallCb) {
console.log("Step2");
insertDocument(db,waterfallCb);
}], function(err,data){
console.log("in waterfall callback");
db.close();
});
输出:
step1
in waterfall callback
为什么第二个函数(打印步骤 2)从未被调用?
编辑:这是 countDocuments:
var countDocuments = function(db,callback){
var collection = db.collection(colname);
collection.find({}).toArray(function(err,docs){
assert.equal(err, null);
console.log("Found %d records",docs.length);
callback(docs);
});
};
编辑:插入文档:
var insertDocument = function(db, callback){
var collection = db.collection(colname);
collection.insertOne(sampleDoc, function(err,result){
assert.equal(err, null);
assert.equal(1, result.result.n);
assert.equal(1, result.ops.length);
console.log("inserted 1 document into the collection");
callback(null, 'one');
});
};
由于您使用 caolan/async
,第一个参数是错误对象,在您的情况下,如果它不是空值,则可能会告诉 async 您有错误并且不再继续。这是文档中的示例:
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
});