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### jsoncons::jsonpath::json_replace
```cpp
#include <jsoncons_ext/jsonpath/json_query.hpp>
```
```cpp
template <typename Json,typename T>
void json_replace(Json& root, const Json::string_view_type& expr, T&& new_value,
result_options options = result_options::nodups); (until 0.164.0)
template <typename Json,typename T>
void json_replace(Json& root, const Json::string_view_type& expr, T&& new_value, (1)
result_options options = result_options::nodups,
const custom_functions<Json>& funcs = custom_functions<Json>()); (since 0.164.0)
template <typename Json,typename T>
void json_replace(Json& root, const Json::string_view_type& expr, T&& new_value,
const custom_functions<Json>& funcs = custom_functions<Json>()); (since 0.171.0)
```
```cpp
template <typename Json,typename BinaryCallback>
void json_replace(Json& root, const Json::string_view_type& expr, BinaryCallback callback,
result_options options = result_options::nodups); (until 0.164.0)
template <typename Json,typename BinaryCallback> (2)
void json_replace(Json& root, const Json::string_view_type& expr, BinaryCallback callback,
result_options options = result_options::nodups,
const custom_functions<Json>& funcs = custom_functions<Json>()); (since 0.164.0)
template <typename Json,typename BinaryCallback>
void json_replace(Json& root, const Json::string_view_type& expr, BinaryCallback callback,
const custom_functions<Json>& funcs = custom_functions<Json>()); (since 0.171.0)
```
```cpp
template <typename Json,typename T,typename TempAllocator>
void json_replace(const allocator_set<Json::allocator_type,TempAllocator>& alloc_set,
Json& root, const Json::string_view_type& expr, T&& new_value, (3) (since 0.171.0)
const custom_functions<Json>& funcs = custom_functions<Json>());
```
```cpp
template <typename Json,typename BinaryCallback,typename TempAllocator>
void json_replace(const allocator_set<Json::allocator_type,TempAllocator>& alloc_set,
Json& root, const Json::string_view_type& expr, BinaryCallback callback, (4) (since 0.171.0)
const custom_functions<Json>& funcs = custom_functions<Json>());
```
(1) Searches for all values that match the JSONPath expression `expr` and replaces them with the specified value
(2) Searches for all values that match a JSONPath expression `expr` and, for each result,
calls a callback provided by the user with a path and mutable reference to the value.
(3)-(4) Same as (1-2) except that `alloc` is used to allocate memory during expression compilation and evaluation.
#### Parameters
<table>
<tr>
<td><code>root</code></td>
<td>JSON value</td>
</tr>
<tr>
<td><code>expr</code></td>
<td>JSONPath expression string</td>
</tr>
<tr>
<td><code>new_value</code></td>
<td>The value to use as replacement</td>
</tr>
<tr>
<td><code>callback</code> (until 0.161.0)</td>
<td>A function object that accepts a const reference to a Json value
and returns a Json value.
It must have function call signature equivalent to
<br/><br/><code>
Json fun(const Json& val);
</code><br/><br/>
</tr>
<tr>
<td><code>callback</code> (since 0.161.0)</td>
<td>A function object that accepts a path and a reference to a Json value.
It must have function call signature equivalent to
<br/><br/><code>
void fun(const Json::string_view_type& path, Json& val);
</code><br/><br/>
</tr>
</table>
#### Exceptions
Throws a [jsonpath_error](jsonpath_error.md) if JSONPath evaluation fails.
### Examples
The examples use the sample data file `books.json`,
```json
{
"books":
[
{
"category": "fiction",
"title" : "A Wild Sheep Chase",
"author" : "Haruki Murakami",
"price" : 22.72
},
{
"category": "fiction",
"title" : "The Night Watch",
"author" : "Sergei Lukyanenko",
"price" : 23.58
},
{
"category": "fiction",
"title" : "The Comedians",
"author" : "Graham Greene",
"price" : 21.99
},
{
"category": "memoir",
"title" : "The Night Watch",
"author" : "Phillips, David Atlee"
}
]
}
```
#### Change the price of A Wild Sheep Chase
```cpp
#include <fstream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpath/jsonpath.hpp>
using namespace jsoncons;
using namespace jsoncons::jsonpath;
int main()
{
std::ifstream is(/*path_to_books_file*/);
json data = json::parse(is);
jsonpath::json_replace(data,"$.books[?(@.title == 'A Wild Sheep Chase')].price",20.0);
std::cout << pretty_print(data) << "\n\n";
}
```
Output:
```json
{
"books": [
{
"author": "Haruki Murakami",
"category": "fiction",
"price": 20.0,
"title": "A Wild Sheep Chase"
},
{
"author": "Sergei Lukyanenko",
"category": "fiction",
"price": 23.58,
"title": "The Night Watch"
},
{
"author": "Graham Greene",
"category": "fiction",
"price": 21.99,
"title": "The Comedians"
},
{
"author": "Phillips, David Atlee",
"category": "memoir",
"title": "The Night Watch"
}
]
}
```
#### Make a discount on all books
```cpp
#include <cmath>
#include <fstream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpath/jsonpath.hpp>
using namespace jsoncons;
using namespace jsoncons::jsonpath;
int main()
{
std::ifstream is(/*path_to_books_file*/);
json data = json::parse(is);
auto f = [](const std::string& /*location*/, json& price)
{
price = std::round(price.as<double>() - 1.0);
};
// make a discount on all books
jsonpath::json_replace(data, "$.books[*].price", f);
std::cout << pretty_print(data);
}
```
Output:
```json
{
"books": [
{
"author": "Haruki Murakami",
"category": "fiction",
"price": 22.0,
"title": "A Wild Sheep Chase"
},
{
"author": "Sergei Lukyanenko",
"category": "fiction",
"price": 23.0,
"title": "The Night Watch"
},
{
"author": "Graham Greene",
"category": "fiction",
"price": 21.0,
"title": "The Comedians"
},
{
"author": "Phillips, David Atlee",
"category": "memoir",
"title": "The Night Watch"
}
]
}
```
#### Add a missing price
```cpp
#include <cmath>
#include <fstream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpath/jsonpath.hpp>
using namespace jsoncons;
using namespace jsoncons::jsonpath;
int main()
{
std::ifstream is(/*path_to_books_file*/);
json data = json::parse(is);
auto f = [](const std::string& /*location*/, json& book)
{
if (book.at("category") == "memoir" && !book.contains("price"))
{
book.try_emplace("price",140.0);
}
};
jsonpath::json_replace(data, "$.books[*]", f);
std::cout << pretty_print(data);
}
```
Output:
```json
{
"books": [
{
"author": "Haruki Murakami",
"category": "fiction",
"price": 22.72,
"title": "A Wild Sheep Chase"
},
{
"author": "Sergei Lukyanenko",
"category": "fiction",
"price": 23.58,
"title": "The Night Watch"
},
{
"author": "Graham Greene",
"category": "fiction",
"price": 21.99,
"title": "The Comedians"
},
{
"author": "Phillips, David Atlee",
"category": "memoir",
"price": 140.0,
"title": "The Night Watch"
}
]
}
```
|
