嗯，一个有趣的问题。以编程方式constructing nested objects from a property accessor string（或the reverse）并不是什么大问题，即使使用multiple descriptors in parallel 也是如此。它确实变得复杂的是需要迭代的数组；当它在 setter 和 getter 端以及多个并行描述符字符串达到不同级别时，这不再那么有趣了。
所以首先我们需要区分脚本中每个访问器描述的数组级别，并解析文本：
function parse(script) {
return script.split(/\s*[;\r\n]+\s*/g).map(function(line) {
var assignment = line.split(/\s*=\s*/);
return assignment.length == 2 ? assignment : null; // console.warn ???
}).filter(Boolean).map(function(as) {
as = as.map(function(accessor) {
var parts = accessor.split("[]").map(function(part) {
return part.split(".");
});
for (var i=1; i<parts.length; i++) {
// assert(parts[i][0] == "")
var prev = parts[i-1][parts[i-1].length-1];
parts[i][0] = prev.replace(/s$/, ""); // singular :-)
}
return parts;
});
if (as[0].length == 1 && as[1].length > 1) // getter contains array but setter does not
as[0].unshift(["output"]); // implicitly return array (but better throw an error)
return {setter:as[0], getter:as[1]};
});
}
这样，文本输入可以变成可用的数据结构，现在看起来像这样：
[{"setter":[["outputModel","items"],["item","name"]],
"getter":[["items"],["item","name"]]},
{"setter":[["outputModel","items"],["item","sku"]],
"getter":[["items"],["item","skus"],["sku","num"]]}]
getter 已经很好地转换为嵌套循环，例如
for (item of items)
for (sku of item.skus)
… sku.num …;
这正是我们要去的地方。这些规则中的每一个都相对容易处理，复制对象的属性并为数组迭代数组，但这是我们最关键的问题：我们有多个规则。当我们处理迭代多个数组时，基本的解决方案是创建它们的cartesian product，这确实是我们需要的。但是，我们希望对此进行很多限制 - 我们不想在输入中创建所有 names 和所有 nums 的每个组合，而是希望按照它们来自的 item 对它们进行分组。
为此，我们将为包含对象生成器的输出结构构建某种前缀树，其中每个递归再次成为相应输出子结构的树。
function multiGroupBy(arr, by) {
return arr.reduce(function(res, x) {
var p = by(x);
(res[p] || (res[p] = [])).push(x);
return res;
}, {});
}
function group(rules) {
var paths = multiGroupBy(rules, function(rule) {
return rule.setter[0].slice(1).join(".");
});
var res = [];
for (var path in paths) {
var pathrules = paths[path],
array = [];
for (var i=0; i<pathrules.length; i++) {
var rule = pathrules[i];
var comb = 1 + rule.getter.length - rule.setter.length;
if (rule.setter.length > 1) // its an array
array.push({
generator: rule.getter.slice(0, comb),
next: {
setter: rule.setter.slice(1),
getter: rule.getter.slice(comb)
}
})
else if (rule.getter.length == 1 && i==0)
res.push({
set: rule.setter[0],
get: rule.getter[0]
});
else
console.error("invalid:", rule);
}
if (array.length)
res.push({
set: pathrules[0].setter[0],
cross: product(array)
});
}
return res;
}
function product(pathsetters) {
var groups = multiGroupBy(pathsetters, function(pathsetter) {
return pathsetter.generator[0].slice(1).join(".");
});
var res = [];
for (var genstart in groups) {
var creators = groups[genstart],
nexts = [],
nests = [];
for (var i=0; i<creators.length; i++) {
if (creators[i].generator.length == 1)
nexts.push(creators[i].next);
else
nests.push({path:creators[i].path, generator: creators[i].generator.slice(1), next:creators[i].next});
}
res.push({
get: creators[0].generator[0],
cross: group(nexts).concat(product(nests))
});
}
return res;
}
现在，我们的规则集 group(parse(script)) 看起来像这样：
[{
"set": ["outputModel","items"],
"cross": [{
"get": ["items"],
"cross": [{
"set": ["item","name"],
"get": ["item","name"]
}, {
"get": ["item","skus"],
"cross": [{
"set": ["item","sku"],
"get": ["sku","num"]
}]
}]
}]
}]
这是一个我们可以实际使用的结构，因为它现在清楚地传达了如何将所有嵌套数组和其中的对象匹配在一起的意图。
让我们动态地解释它，为给定的输入构建一个输出：
function transform(structure, input, output) {
for (var i=0; i<structure.length; i++) {
output = assign(output, structure[i].set.slice(1), getValue(structure[i], input));
}
return output;
}
function retrieve(val, props) {
return props.reduce(function(o, p) { return o[p]; }, val);
}
function assign(obj, props, val) {
if (!obj)
if (!props.length) return val;
else obj = {};
for (var j=0, o=obj; j<props.length-1 && o!=null && o[props[j]]; o=o[props[j++]]);
obj[props[j]] = props.slice(j+1).reduceRight(function(val, p) {
var o = {};
o[p] = val;
return o;
}, val);
return obj;
}
function getValue(descriptor, input) {
if (descriptor.get) // && !cross
return retrieve(input, descriptor.get.slice(1));
var arr = [];
descriptor.cross.reduce(function horror(next, d) {
if (descriptor.set)
return function (inp, cb) {
next(inp, function(res){
cb(assign(res, d.set.slice(1), getValue(d, inp)));
});
};
else // its a crosser
return function(inp, cb) {
var g = retrieve(inp, d.get.slice(1)),
e = d.cross.reduce(horror, next)
for (var i=0; i<g.length; i++)
e(g[i], cb);
};
}, function innermost(inp, cb) {
cb(); // start to create an item
})(input, function(res) {
arr.push(res); // store the item
});
return arr;
}
这确实适用于
var result = transform(group(parse(script)), items); // your expected result
但我们可以做得更好，性能更高：
function compile(structure) {
function make(descriptor) {
if (descriptor.get)
return {inputName: descriptor.get[0], output: descriptor.get.join(".") };
var outputName = descriptor.set[descriptor.set.length-1];
var loops = descriptor.cross.reduce(function horror(next, descriptor) {
if (descriptor.set)
return function(it, cb) {
return next(it, function(res){
res.push(descriptor)
return cb(res);
});
};
else // its a crosser
return function(it, cb) {
var arrName = descriptor.get[descriptor.get.length-1],
itName = String.fromCharCode(it);
var inner = descriptor.cross.reduce(horror, next)(it+1, cb);
return {
inputName: descriptor.get[0],
statement: (descriptor.get.length>1 ? "var "+arrName+" = "+descriptor.get.join(".")+";\n" : "")+
"for (var "+itName+" = 0; "+itName+" < "+arrName+".length; "+itName+"++) {\n"+
"var "+inner.inputName+" = "+arrName+"["+itName+"];\n"+
inner.statement+
"}\n"
};
};
}, function(_, cb) {
return cb([]);
})(105, function(res) {
var item = joinSetters(res);
return {
inputName: item.inputName,
statement: (item.statement||"")+outputName+".push("+item.output+");\n"
};
});
return {
statement: "var "+outputName+" = [];\n"+loops.statement,
output: outputName,
inputName: loops.inputName
};
}
function joinSetters(descriptors) {
if (descriptors.length == 1 && descriptors[0].set.length == 1)
return make(descriptors[0]);
var paths = multiGroupBy(descriptors, function(d){ return d.set[1] || console.error("multiple assignments on "+d.set[0], d); });
var statements = [],
inputName;
var props = Object.keys(paths).map(function(p) {
var d = joinSetters(paths[p].map(function(d) {
var names = d.set.slice(1);
names[0] = d.set[0]+"_"+names[0];
return {set:names, get:d.get, cross:d.cross};
}));
inputName = d.inputName;
if (d.statement)
statements.push(d.statement)
return JSON.stringify(p) + ": " + d.output;
});
return {
inputName: inputName,
statement: statements.join(""),
output: "{"+props.join(",")+"}"
};
}
var code = joinSetters(structure);
return new Function(code.inputName, code.statement+"return "+code.output+";");
}
所以这就是你最终会得到的：
> var example = compile(group(parse("outputModel.items[].name = items[].name;outputModel.items[].sku = items[].skus[].num;")))
function(items) {
var outputModel_items = [];
for (var i = 0; i < items.length; i++) {
var item = items[i];
var skus = item.skus;
for (var j = 0; j < skus.length; j++) {
var sku = skus[j];
outputModel_items.push({"name": item.name,"sku": sku.num});
}
}
return {"items": outputModel_items};
}
> var flatten = compile(group(parse("as[]=bss[][]")))
function(bss) {
var as = [];
for (var i = 0; i < bss.length; i++) {
var bs = bss[i];
for (var j = 0; j < bs.length; j++) {
var b = bs[j];
as.push(b);
}
}
return as;
}
> var parallelRecords = compile(group(parse("x.as[]=y[].a; x.bs[]=y[].b")))
function(y) {
var x_as = [];
for (var i = 0; i < y.length; i++) {
var y = y[i];
x_as.push(y.a);
}
var x_bs = [];
for (var i = 0; i < y.length; i++) {
var y = y[i];
x_bs.push(y.b);
}
return {"as": x_as,"bs": x_bs};
}
现在您可以轻松地将输入数据传递给动态创建的函数，它会很快被转换:-)