Loading JSON array from file
Adding a new object to the existing list
Saving the list to a new file
Useful resources
Introduction
In my previous article, I covered
serializing/deserializing JSON
in C++ to a simple object using
RapidJSON
.
When working with JSON, my goal is to work always with object models and keep the actual JSON parsing behind the scenes. This keeps the readability and maintainability of the code as JSON manipulation, type checking and exception handling is done is a single class and not across the entire application. This also enables a future replacement of the JSON parsing library without the need to change the code of the entire application.
My stack
Visual Studio 2019 Community Edition, 16.5.1
RapidJSON 1.1.0 release
Windows 10 Pro 64-bit (10.0, Build 18363)
Preparing the project
I am going to use the same C++ Console Application from the previous post about
JSON Serialization in C++
.
My JSON will be an array of products in an inventory. Here is the sample of 3 products in inventory:
3
"id"
:
1
,
4
"name"
:
"Bush Somerset Collection Bookcase"
,
5
"category"
:
"Furniture"
,
6
"sales"
:
22.0
7
},
9
"id"
:
2
,
10
"name"
:
"Mitel 5320 IP Phone VoIP phone"
,
11
"category"
:
"Technology"
,
12
"sales"
:
907.1519775390625
13
},
14
{
15
"id"
:
3
,
16
"name"
:
"Poly String Tie Envelopes"
,
17
"category"
:
"Office Supplies"
,
18
"sales"
:
3.2639999389648439
19
}
Creating the object models
For the single product, we used the following object model:
We added member variable for every JSON property with the correct type (id, name, sales, category)
Implemented getters/setters
Implemented Serialize and Deserialize functions
1namespace JSONModels
3 class Product : public JSONBase
5 public:
6 Product();
7 virtual ~Product();
9 virtual bool Deserialize(const rapidjson::Value& obj);
10 virtual bool Serialize(rapidjson::Writer<rapidjson::StringBuffer>* writer) const;
12 // Getters/Setters.
13 const std::string& Name() const { return _name; }
14 void Name(const std::string& name) { _name = name; }
16 const std::string& Category() const { return _category; }
17 void Category(const std::string& category) { _category = category; }
19 float Sales() const { return _sales; }
20 void Sales(float sales) { _sales = sales; }
22 int Id() const { return _id; }
23 void Id(int id) { _id = id; }
24 private:
25 std::string _name;
26 std::string _category;
27 float _sales;
28 int _id;
29 };
In the next step, we need to create a class that will hold a list of
Product
objects.
1namespace JSONModels
3 class Products : public JSONBase
5 public:
6 virtual ~Products() {};
7 virtual bool Deserialize(const std::string& s);
9 // Getters/Setters.
10 std::list<Product>& ProductsList() { return _products; }
11 public:
12 virtual bool Deserialize(const rapidjson::Value& obj) { return false; };
13 virtual bool Serialize(rapidjson::Writer<rapidjson::StringBuffer>* writer) const;
14 private:
15 std::list<Product> _products;
16 };
Serialize
This function is called by JSONBase class once the object is being serialized. Our list is stored in the memory, so we need to write it to the
StringBuffer
.
In this code, we iterate over all Product in our
_product
list and call for Serialize function of the Product class.
1bool Products::Serialize(rapidjson::Writer<rapidjson::StringBuffer>* writer) const
3 writer->StartArray();
5 for (std::list<Product>::const_iterator it = _products.begin(); it != _products.end(); it++)
7 (*it).Serialize(writer);
9 writer->EndArray();
11 return true;
Deserialize
Deserialize function is called by JSONBase class with JSON string parameter.
First we need to call for
InitDocument
function to parse the string
Once the
doc
object is initialized, we need to iterate over all JSON objects, call for Deserialize and finally add to
_products
list.
1bool Products::Deserialize(const std::string& s)
3 rapidjson::Document doc;
4 if (!InitDocument(s, doc))
5 return false;
7 if (!doc.IsArray())
8 return false;
10 for (rapidjson::Value::ConstValueIterator itr = doc.Begin(); itr != doc.End(); ++itr)
11 {
12 Product p;
13 p.Deserialize(*itr);
14 _products.push_back(p);
15 }
17 return true;
Usage
Loading JSON array from file
1// load json array
2JSONModels::Products products;
3products.DeserializeFromFile("DataSampleArray.json");
5for (std::list<JSONModels::Product>::const_iterator it = products.ProductsList().begin();
6 it != products.ProductsList().end(); it++)
8 // print some values.
9 printf("Name:%s, Sales:%.3f", (*it).Name().c_str(), (*it).Sales());
Adding a new object to the existing list
1// add new product
2JSONModels::Product newProduct;
3newProduct.Id(101);
4newProduct.Name("Global Value Mid-Back Manager's Chair, Gray");
5newProduct.Category("Furniture");
6newProduct.Sales(213.115f);
7products.ProductsList().push_back(product);
Saving the list to a new file
1// save to new array file.
2products.SerializeToFile("DataSampleArrayNew.json")
Useful resources
Full source code of this post in
GitHub
