Mongo API for C++
This is an attempt to have a simple to use Type-Safe API to connect and manipulate data on a MongoDB Server.
This API does not currently implement the full MongoDB API, but rather the subset of the API around data manipulation and storage.
This library makes heavy use of ThorSerialize API to automate the generation of the BSON documents that are exchanged between the application and the MongoDB Server. The advantage of this library is that no code needs to be written to create or generate BSON objects (this is all automated).
These libraries are available via brew
> brew install thors-mongoBuild and install the libraries manually:
> git clone [email protected]:Loki-Astari/ThorsMongo.git
> cd ThorsMongo
> ./configure
> make
> make installNote: The configuration script should check for all dependencies and give instructions on how to fix any issues.
There is a header only version. You will need to install it and a couple of other libraries manually.
> git clone --single-branch --branch header-only [email protected]:Loki-Astari/ThorsMongo.git
> git clone [email protected]:Neargye/magic_enum
> # or brew install magic_enum
> brew install snappyLook at the Example folder for example of how to build against this project. This project also includes all the code on this page.
All communication done with the MongoDB Server id done via the ThorsMongo class.
#include "ThorsMongo/ThorsMongo.h"
// Connecting to MongoDB
using ThorsAnvil::DB::Mongo::ThorsMongo;
ThorsMongo mongo({"localhost", 27017}, {"usernmae", "password", "DB"});Note: I have currently only implemented SCRAM-SHA-256 authentication mechanism. So the user must have this enabled.
// Mongo Shell
DB> show users
[
{
_id: 'DB.username',
userId: UUID('eb180bc7-6347-4cf9-8f5c-9aaf7236b3a9'),
user: 'username',
db: 'DB',
roles: [
{ role: 'dbAdmin', db: 'DB' }
],
mechanisms: [ 'SCRAM-SHA-256' ]
^^^^^^^^^^^^^^^^^^ Please check your user has this enabled.
}
]On a MongoDB Server there are multiple Databases. Each Database can have multiple Collections. There are appropriate class for these types of object.
ThorsAnvil::DB::Mongo::DBThorsAnvil::DB::Mongo::Collection
using ThorsAnvil::DB::Mongo::DB;
using ThorsAnvil::DB::Mogno::Collection;
DB db(mongo, "DB");
Collection collection(db, "People");
// For convenience the [] operator have been overloaded to give you accesses to these objects.
// without the need to create local objects.
mongo["DB"].method(); // Has same affect as: db.method();
mongo["DB"]["People"].method(); // Has same effect as: db["People"].method()
// and: collection.method();You can insert any data you like into a collection.
To serialize the data you must declare the class you are sending to MongoDB as serializable (using ThorsSerialize ). This has a tiny bit of boilerplate declaration per class. I provide a simple example here. More detailed examples and documentation can be found here.
// The structure I want to store.
// C++ class declarations.
class Address
{
// To give the serializer accesses to private data.
friend class ThorsAnvil::Serialize::Traits<Address>;
std::string street1;
std::string street2;
std::string city;
std::string country;
std::string postCode;
public:
Address(std::string const& street1, std::string const& street2, std::string const& city, std::string const& country, std::string const& postCode)
: street1(street1)
, street2(street2)
, city(city)
, country(country)
, postCode(postCode)
{}
};
class Person
{
// To give the serializer accesses to private data.
friend class ThorsAnvil::Serialize::Traits<Person>;
std::string name;
std::uint32_t age;
std::vector<std::string> alergies;
Address address;
public:
Person(std::string const& name, std::uint32_t age, Address const& address)
: name(name)
, age(age)
, address(address)
{}
};
// Declare the types serializable using ThorsSerialize
// All POD types can be serialized.
// All types in the standard library can be serialized.
// A declaration is need for each custom type you want to serialize.
ThorsAnvil_MakeTrait(Address, street1, street2, city, country, postCode);
ThorsAnvil_MakeTrait(Person, name, age, alergies, address);To insert data into a collection call the insert() method passing either a vector or a tuple of objects. Note: The types of all the objects have to be serializable.
void addPeopleToMongo(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::vector<Person> const& people)
{
// The insert() method takes either
// 1: a vector of any object that can be serialized.
// 2: a tuple of objects that can be serialized.
auto result = mongo["DB"]["Collection"].insert(people);
if (result)
{
// Data was inserted successfully
std::cout << "Inserted ID:\n";
for (auto const& id: result.inserted)
{
std::cout << "\t" << id << "\n";
}
}
else
{
std::cout << "Error: " << result << "\n";
}
}If you only want to insert a single item you can invisibly create a vector by wrapping the object in curly braces.
auto result = mongo["DB"]["Collection"].insert({ aSinglePersonObject });To find data you must specify a "Filter".
This requires some boilerplate to allow you to match against specific fields in your data. I will provide a simple examples here. Details will be provided below in the Query documentation.
The find() method takes a filter and returns a C++ range.
// This macro creates a type called "FindEqName"
// It can be used to filter records by Person.name on the server using "Eq" (Equality)
ThorsMongo_CreateFieldAccess(Person, name);
using FindEqName = ThorsMongo_FilterFromAccess(Eq, Person, age);
void findPeopleInMongoByName(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::string const& name)
{
// Returns a C++ range of all the objects that match the query.
// Note: The range hides a MongoDB cursor so as you you iterate across the query
// this may result in more calls to MongoDB to retrieve more data automatically.
auto range = mongo["DB"]["Collection"].find<Person>(FindEqName{name});
if (range)
{
// Print all the returned people
for (auto const& person: range) {
std::cout << ThorsAnvil::Serialize::jsonExporter(person);
}
}
else
{
std::cout << "Error: " << range << "\n";
}
}The remove method operates on a Query. This is basically a "Filter" with an extra parameter indicating if the remove should apply to the first or all matches. The example below shows remove using a single Query object, but this method can take any number of Query objects that are all applied in parallel.
Note: If you are only deleting one and the filter matches multiple records in the collection then you are effectively deleting a random matching record. Please read the full documentation to understand how to control the filter to get an exact match or use findAndRemoveOne() method for more control.
// Create a filter on Person.age using the "Gt" (Greater than) operator
ThorsMongo_CreateFieldAccess(Person, age);
using FindGtAge = ThorsMongo_FilterFromAccess(Gt, Person, age);
void removePeopelFromMongoByName(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::uint32_t minAge, bool removeOne)
{
using ThorsAnvil::DB::Mongo::Query;
using ThorsAnvil::DB::Mongo::Remove;
auto result = mongo["test"]["People"].remove(Query<FindGtAge>{minAge, removeOne ? Remove::One : Remove::All});
if (result)
{
std::cerr << "Removed: " << result.n << "\n";
}
else
{
std::cerr << "Error: " << result << "\n";
}
};There is a family of functions to find and modify a single record.
- findAndReplaceOne();
- findAndRemoveOne();
- findAndUpdateOne();
All these functions use a "Filter" to select a single record. If your filter matches multiple records you can add a sort order (the first item in the sorted results is modified. See full documentation for details).
The findAndReplaceOne() methods find and update a single record using a "Filter" and replaces the record with a new record. This is useful if all the updates are done in the application side.
void replacePerson(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::string const& name, Person const& p)
{
auto result = mongo["test"]["People"].findAndReplaceOne(FindEqName{name}, p);
if (result)
{
if (!result.value)
{
std::cerr << "No original value\n";
}
else
{
std::cerr << "Orginal Value: " << ThorsAnvil::Serialize::jsonExporter(*result.value) << "\n";
}
}
else
{
std::cerr << "Error: " << result << "\n";
}
}The findAndRemoveOne() methods find and removes a single record using a "Filter".
void removePerson(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::string const& name)
{
auto result = mongo["test"]["People"].findAndRemoveOne<Person>(FindEqName{name});
if (result)
{
if (!result.value)
{
std::cerr << "No original value\n";
}
else
{
std::cerr << "Orginal Value: " << ThorsAnvil::Serialize::jsonExporter(*result.value) << "\n";
}
}
else
{
std::cerr << "Error: " << result << "\n";
}
}The findAndUpdateOne() methods find a single record using a "Filter" and then applies a custom update operation on the server side. This can simplify the client code and allow updates to parts of the document on the server without having to download the data onto the client.
The update is expressed as an "Expression" that requires some boilerplate. I will provide a simple example here. Details will be provided below in the Update documentation.
// This macro creates a type called "SetAge"
// It will "Set" the value of Person.age on the server.
ThorsMongo_CreateFieldAccess(Person, age);
using SetAge = ThorsMongo_UpdateFromAccess(Set, Person, age);
void updateAddressCity(ThorsAnvil::DB::Mongo::ThorsMongo& mongo, std::string const& name, std::uint32_t newAge)
{
using ThorsAnvil::DB::Mongo::Query;
using ThorsAnvil::DB::Mongo::Remove;
auto result = mongo["test"]["People"].findAndUpdateOne<Person>(FindEqName{name}, SetAge{newAge});
if (result)
{
if (!result.value)
{
std::cerr << "No original value\n";
}
else
{
std::cerr << "Orginal Value: " << ThorsAnvil::Serialize::jsonExporter(*result.value) << "\n";
}
}
else
{
std::cerr << "Error: " << result << "\n";
}
};