使用mongo c ++驱动程序查询嵌套的BSON文档 [英] Query nested BSON documents with mongo c++ driver
问题描述
我有一个bsoncxx::document::view bsonObjView和std::vector<std::string> path，它们代表我们要在BSON文档中搜索的值的键(第一个键是顶层，第二个键是深度1，第三个键深度2等). /p>
我正在尝试编写一个给定路径的函数，该函数将搜索bson文档:
bsoncxx::document::element deepFieldAccess(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
assert (!path.empty());
// for each key, find the corresponding value at the current depth, next keys will search the value (document) we found at the current depth
for (auto const& currKey: path) {
// get value for currKey
bsonObj = bsonObj.find(currKey);
}
// for every key in the path we found a value at the appropriate level, we return the final value we found with the final key
return bsonObj;
}
如何使该功能起作用? bsonObj应该允许哪种类型的循环搜索?另外，如何检查是否找到currKey的值?
此外，是否有一些 bsoncxx 来实现此目的?
这是一个示例json文档，后跟一些指向其中的值的路径.给定路径时，最终解决方案应返回相应的值:
{
"shopper": {
"Id": "4973860941232342",
"Context": {
"CollapseOrderItems": false,
"IsTest": false
}
},
"SelfIdentifiersData": {
"SelfIdentifierData": [
{
"SelfIdentifierType": {
"SelfIdentifierType": "111"
}
},
{
"SelfIdentifierType": {
"SelfIdentifierType": "2222"
}
}
]
}
}
示例路径:
路径[ shopper -> Id -> targetValue ]指向字符串"4973860941232342".
路径[ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> targetValue ]指向对象{ "SelfIdentifierType": { "SelfIdentifierType": "111" } }.
路径[ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> SelfIdentifierType -> targetValue ]指向对象{ "SelfIdentifierType": "111" }.
路径[ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> SelfIdentifierType -> SelfIdentifierType -> targetValue ]指向字符串"111".
请注意，路径的类型为std::vector<std::string> path.因此，最终解决方案应返回路径指向的值.它应该适用于任意深度，也适用于指向TO数组元素的路径(第二个示例路径)和THROUGH数组元素的路径(最后两个示例路径).我们假定索引为i的数组元素的键为"i".
更新:当前，@ acm建议的方法无法用于具有数组索引的路径(没有数组索引的路径可以正常工作).这是重现此问题的所有代码:
#include <iostream>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
std::string turnQueryResultIntoString3(bsoncxx::document::element queryResult) {
// check if no result for this query was found
if (!queryResult) {
return "[NO QUERY RESULT]";
}
// hax
bsoncxx::builder::basic::document basic_builder{};
basic_builder.append(bsoncxx::builder::basic::kvp("Your Query Result is the following value ", queryResult.get_value()));
std::string rawResult = bsoncxx::to_json(basic_builder.view());
std::string frontPartRemoved = rawResult.substr(rawResult.find(":") + 2);
std::string backPartRemoved = frontPartRemoved.substr(0, frontPartRemoved.size() - 2);
return backPartRemoved;
}
// TODO this currently fails for paths with array indices
bsoncxx::document::element deepFieldAccess3(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
if (path.empty())
return {};
auto keysIter = path.begin();
const auto keysEnd = path.end();
std::string currKey = *keysIter; // for debug purposes
std::cout << "Current key: " << currKey;
auto currElement = bsonObj[*(keysIter++)];
std::string currElementAsString = turnQueryResultIntoString3(currElement); // for debug purposes
std::cout << " Query result for this key: " << currElementAsString << std::endl;
while (currElement && (keysIter != keysEnd)) {
currKey = *keysIter;
std::cout << "Current key: " << currKey;
currElement = currElement[*(keysIter++)];
currElementAsString = turnQueryResultIntoString3(currElement);
std::cout << " Query result for this key: " << currElementAsString << std::endl;
}
return currElement;
}
// execute this function to see that queries with array indices fail
void reproduceIssue() {
std::string testJson = "{\n"
" \"shopper\": {\n"
" \"Id\": \"4973860941232342\",\n"
" \"Context\": {\n"
" \"CollapseOrderItems\": false,\n"
" \"IsTest\": false\n"
" }\n"
" },\n"
" \"SelfIdentifiersData\": {\n"
" \"SelfIdentifierData\": [\n"
" {\n"
" \"SelfIdentifierType\": {\n"
" \"SelfIdentifierType\": \"111\"\n"
" }\n"
" },\n"
" {\n"
" \"SelfIdentifierType\": {\n"
" \"SelfIdentifierType\": \"2222\"\n"
" }\n"
" }\n"
" ]\n"
" }\n"
"}";
// create bson object
bsoncxx::document::value bsonObj = bsoncxx::from_json(testJson);
bsoncxx::document::view bsonObjView = bsonObj.view();
// example query which contains an array index, this fails. Expected query result is "111"
std::vector<std::string> currQuery = {"SelfIdentifiersData", "SelfIdentifierData", "0", "SelfIdentifierType", "SelfIdentifierType"};
// an example query without array indices, this works. Expected query result is "false"
//std::vector<std::string> currQuery = {"shopper", "Context", "CollapseOrderItems"};
bsoncxx::document::element queryResult = deepFieldAccess3(bsonObjView, currQuery);
std::cout << "\n\nGiven query and its result: [ ";
for (auto i: currQuery)
std::cout << i << ' ';
std::cout << "] -> " << turnQueryResultIntoString3(queryResult) << std::endl;
}
没有内置的方法可以执行此操作，因此您将需要编写一个上面概述的辅助函数.
我相信您遇到的问题是该函数的参数是bsoncxx::document::view，但是view::find的返回值是bsoncxx::document::element.因此，您需要考虑循环中某处的类型更改.
我想我会这样写函数:
bsoncxx::document::element deepFieldAccess(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
if (path.empty())
return {};
auto keysIter = path.begin();
const auto keysEnd = path.end();
auto currElement = bsonObj[*(keysIter++)];
while (currElement && (keysIter != keysEnd))
currElement = currElement[*(keysIter++)];
return currElement;
}
请注意，如果找不到路径的任何部分，或者如果路径尝试遍历到实际上不是BSON文档或BSON数组的对象，则这将返回无效的bsoncxx::document::element.
I have a bsoncxx::document::view bsonObjViewand a std::vector<std::string> path that represents keys to the value we are searching for in the BSON document (first key is top level, second key is depth 1, third key depth 2, etc).
I'm trying to write a function that given a path will search the bson document:
bsoncxx::document::element deepFieldAccess(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
assert (!path.empty());
// for each key, find the corresponding value at the current depth, next keys will search the value (document) we found at the current depth
for (auto const& currKey: path) {
// get value for currKey
bsonObj = bsonObj.find(currKey);
}
// for every key in the path we found a value at the appropriate level, we return the final value we found with the final key
return bsonObj;
}
How to make the function work? What type should bsonObjbe to allow for such searches within a loop? Also, how to check if a value for currKey has been found?
Also, is there some bsoncxx built in way to do this?
Here is an example json document followed by some paths that point to values inside of it. The final solution should return the corresponding value when given the path:
{
"shopper": {
"Id": "4973860941232342",
"Context": {
"CollapseOrderItems": false,
"IsTest": false
}
},
"SelfIdentifiersData": {
"SelfIdentifierData": [
{
"SelfIdentifierType": {
"SelfIdentifierType": "111"
}
},
{
"SelfIdentifierType": {
"SelfIdentifierType": "2222"
}
}
]
}
}
Example paths:
The path [ shopper -> Id -> targetValue ] points to the string "4973860941232342".
The path [ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> targetValue ] points to the object { "SelfIdentifierType": { "SelfIdentifierType": "111" } }.
The path [ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> SelfIdentifierType -> targetValue ] points to the object { "SelfIdentifierType": "111" }.
The path [ SelfIdentifiersData -> SelfIdentifierData -> array_idx: 0 -> SelfIdentifierType -> SelfIdentifierType -> targetValue ] points to the string "111".
Note that the paths are of the type std::vector<std::string> path. So the final solution should return the value that the path points to. It should work for arbitrary depths, and also for paths that point TO array elements (second example path) and THROUGH array elements (last 2 example paths). We assume that the key for an array element at index i is "i".
Update: Currently, the approach suggested by @acm fails for paths with array indices (paths without array indices work fine). Here is all the code to reproduce the issue:
#include <iostream>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
std::string turnQueryResultIntoString3(bsoncxx::document::element queryResult) {
// check if no result for this query was found
if (!queryResult) {
return "[NO QUERY RESULT]";
}
// hax
bsoncxx::builder::basic::document basic_builder{};
basic_builder.append(bsoncxx::builder::basic::kvp("Your Query Result is the following value ", queryResult.get_value()));
std::string rawResult = bsoncxx::to_json(basic_builder.view());
std::string frontPartRemoved = rawResult.substr(rawResult.find(":") + 2);
std::string backPartRemoved = frontPartRemoved.substr(0, frontPartRemoved.size() - 2);
return backPartRemoved;
}
// TODO this currently fails for paths with array indices
bsoncxx::document::element deepFieldAccess3(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
if (path.empty())
return {};
auto keysIter = path.begin();
const auto keysEnd = path.end();
std::string currKey = *keysIter; // for debug purposes
std::cout << "Current key: " << currKey;
auto currElement = bsonObj[*(keysIter++)];
std::string currElementAsString = turnQueryResultIntoString3(currElement); // for debug purposes
std::cout << " Query result for this key: " << currElementAsString << std::endl;
while (currElement && (keysIter != keysEnd)) {
currKey = *keysIter;
std::cout << "Current key: " << currKey;
currElement = currElement[*(keysIter++)];
currElementAsString = turnQueryResultIntoString3(currElement);
std::cout << " Query result for this key: " << currElementAsString << std::endl;
}
return currElement;
}
// execute this function to see that queries with array indices fail
void reproduceIssue() {
std::string testJson = "{\n"
" \"shopper\": {\n"
" \"Id\": \"4973860941232342\",\n"
" \"Context\": {\n"
" \"CollapseOrderItems\": false,\n"
" \"IsTest\": false\n"
" }\n"
" },\n"
" \"SelfIdentifiersData\": {\n"
" \"SelfIdentifierData\": [\n"
" {\n"
" \"SelfIdentifierType\": {\n"
" \"SelfIdentifierType\": \"111\"\n"
" }\n"
" },\n"
" {\n"
" \"SelfIdentifierType\": {\n"
" \"SelfIdentifierType\": \"2222\"\n"
" }\n"
" }\n"
" ]\n"
" }\n"
"}";
// create bson object
bsoncxx::document::value bsonObj = bsoncxx::from_json(testJson);
bsoncxx::document::view bsonObjView = bsonObj.view();
// example query which contains an array index, this fails. Expected query result is "111"
std::vector<std::string> currQuery = {"SelfIdentifiersData", "SelfIdentifierData", "0", "SelfIdentifierType", "SelfIdentifierType"};
// an example query without array indices, this works. Expected query result is "false"
//std::vector<std::string> currQuery = {"shopper", "Context", "CollapseOrderItems"};
bsoncxx::document::element queryResult = deepFieldAccess3(bsonObjView, currQuery);
std::cout << "\n\nGiven query and its result: [ ";
for (auto i: currQuery)
std::cout << i << ' ';
std::cout << "] -> " << turnQueryResultIntoString3(queryResult) << std::endl;
}
There is not a built-in way to to do this, so you will need to write a helper function like the one you outline above.
I believe the issue you are encountering is that the argument to the function is a bsoncxx::document::view, but the return value of view::find is a bsoncxx::document::element. So you need to account for the change of type somewhere in the loop.
I think I would write the function this way:
bsoncxx::document::element deepFieldAccess(bsoncxx::document::view bsonObj, const std::vector<std::string>& path) {
if (path.empty())
return {};
auto keysIter = path.begin();
const auto keysEnd = path.end();
auto currElement = bsonObj[*(keysIter++)];
while (currElement && (keysIter != keysEnd))
currElement = currElement[*(keysIter++)];
return currElement;
}
Note that this will return an invalid bsoncxx::document::element if any part of the path is not found, or if the path attempts to traverse into an object that is not a actually a BSON document or BSON array.
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