# sqlite_modern_cpp

**Repository Path**: dqsjqian/sqlite_modern_cpp

## Basic Information

- **Project Name**: sqlite_modern_cpp
- **Description**: No description available
- **Primary Language**: C++
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2020-04-24
- **Last Updated**: 2024-11-04

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

[![Build Status](https://drone.io/github.com/aminroosta/sqlite_modern_cpp/status.png)](https://drone.io/github.com/aminroosta/sqlite_modern_cpp/latest)

sqlite modern cpp wrapper
====

This library is a lightweight modern wrapper around sqlite C api .

```c++
#include<iostream>
#include <sqlite_modern_cpp.h>
using namespace  sqlite;
using namespace std;

int main() {

   try {
      // creates a database file 'dbfile.db' if it does not exists.
      database db("dbfile.db");

      // executes the query and creates a 'user' table
      db <<
         "create table if not exists user ("
         "   _id integer primary key autoincrement not null,"
         "   age int,"
         "   name text,"
         "   weight real"
         ");";

      // inserts a new user record.
      // binds the fields to '?' .
      // note that only types allowed for bindings are :
      //      int ,long, long long, float, double
      //      string , u16string
      // sqlite3 only supports utf8 and utf16 strings, you should use std::string for utf8 and std::u16string for utf16.
      // note that u"my text" is a utf16 string literal of type char16_t * .
      db << "insert into user (age,name,weight) values (?,?,?);"
         << 20
         << u"bob"
         << 83.25;

      int age = 21;
      float weight = 68.5;
      string name = "jack";
      db << u"insert into user (age,name,weight) values (?,?,?);" // utf16 query string
         << age
         << name
         << weight;

      cout << "The new record got assigned id " << db.last_insert_rowid() << endl;

      // slects from user table on a condition ( age > 18 ) and executes
      // the lambda for each row returned .
      db << "select age,name,weight from user where age > ? ;"
         << 18
         >> [&](int age, string name, double weight) {
            cout << age << ' ' << name << ' ' << weight << endl;
         };

      // selects the count(*) from user table
      // note that you can extract a single culumn single row result only to : int,long,long,float,double,string,u16string
      int count = 0;
      db << "select count(*) from user" >> count;
      cout << "cout : " << count << endl;

      // you can also extract multiple column rows
      db << "select age, name from user where _id=1;" >> tie(age, name);
      cout << "Age = " << age << ", name = " << name << endl;

      // this also works and the returned value will be automatically converted to string
      string str_count;
      db << "select count(*) from user" >> str_count;
      cout << "scount : " << str_count << endl;
   }
   catch (exception& e) {
      cout << e.what() << endl;
   }
}
```

You can not execute multiple statements separated by semicolons in one go.

Additional flags
----
You can pass additional open flags to SQLite by using a config object:

```c++
sqlite_config config;
config.flags = OpenFlags::READONLY
database db("some_db", config);
int a;
// Now you can only read from db
auto ps = db << "select a from table where something = ? and anotherthing = ?" >> a;
config.flags = OpenFlags::READWRITE | OpenFlags::CREATE; // This is the default
config.encoding = Encoding::UTF16; // The encoding is respected only if you create a new database
database db2("some_db2", config);
// If some_db2 didn't exists before, it will be created with UTF-16 encoding.
```

Prepared Statements
----
It is possible to retain and reuse statments this will keep the query plan and in case of an complex query or many uses might increase the performance significantly.

```c++
database db(":memory:");

// if you use << on a sqlite::database you get a prepared statment back
// this will not be executed till it gets destroyed or you execute it explicitly
auto ps = db << "select a,b from table where something = ? and anotherthing = ?"; // get a prepared parsed and ready statment

// first if needed bind values to it
ps << 5;
int tmp = 8;
ps << tmp;

// now you can execute it with `operator>>` or `execute()`.
// If the statement was executed once it will not be executed again when it goes out of scope.
// But beware that it will execute on destruction if it wasn't executed!
ps >> [&](int a,int b){ ... };

// after a successfull execution the statment can be executed again, but the bound values are resetted.
// If you dont need the returned values you can execute it like this
ps++; // Does reset the bound values
// or like this
ps.execute(); // Does NOT reset the bound values, but we can reset them manually:
ps.reset();

// To disable the execution of a statment when it goes out of scope and wasn't used
ps.used(true); // or false if you want it to execute even if it was used

// Usage Example:

auto ps = db << "insert into complex_table_with_lots_of_indices values (?,?,?)";
int i = 0;
while( i < 100000 ){
   ps << long_list[i++] << long_list[i++] << long_list[i++];
   ps++; // Equal to: ps.execute(); ps.reset();
}
```

Shared Connections
----
If you need the handle to the database connection to execute sqlite3 commands directly you can get a managed shared_ptr to it, so it will not close as long as you have a referenc to it.

Take this example on how to deal with a database backup using SQLITEs own functions in a safe and modern way.
```c++
try {
   database backup("backup");		//Open the database file we want to backup to

   auto con = db.connection();   // get a handle to the DB we want to backup in our scope
                                 // this way we are sure the DB is open and ok while we backup

   // Init Backup and make sure its freed on exit or exceptions!
   auto state =
      std::unique_ptr<sqlite3_backup,decltype(&sqlite3_backup_finish)>(
      sqlite3_backup_init(backup.connection().get(), "main", con.get(), "main"),
      sqlite3_backup_finish
      );

   if(state) {
      int rc;
      // Each iteration of this loop copies 500 database pages from database db to the backup database.
      do {
         rc = sqlite3_backup_step(state.get(), 500);
         std::cout << "Remaining " << sqlite3_backup_remaining(state.get()) << "/" << sqlite3_backup_pagecount(state.get()) << "\n";
      } while(rc == SQLITE_OK || rc == SQLITE_BUSY || rc == SQLITE_LOCKED);
   }
} // Release allocated resources.
```

Transactions
----
You can use transactions with `begin;`, `commit;` and `rollback;` commands.

```c++
db << "begin;"; // begin a transaction ...   
db << "insert into user (age,name,weight) values (?,?,?);"
   << 20
   << u"bob"
   << 83.25f;
db << "insert into user (age,name,weight) values (?,?,?);" // utf16 string
   << 21
   << u"jack"
   << 68.5;
db << "commit;"; // commit all the changes.

db << "begin;"; // begin another transaction ....
db << "insert into user (age,name,weight) values (?,?,?);" // utf16 string
   << 19
   << u"chirs"
   << 82.7;
db << "rollback;"; // cancel this transaction ...

```

Blob
----
Use `std::vector<T>` to store and retrieve blob data.  
`T` could be `char,short,int,long,long long, float or double`.

```c++
db << "CREATE TABLE person (name TEXT, numbers BLOB);";
db << "INSERT INTO person VALUES (?, ?)" << "bob" << vector<int> { 1, 2, 3, 4};
db << "INSERT INTO person VALUES (?, ?)" << "sara" << vector<double> { 1.0, 2.0, 3.0, 4.0};

vector<int> numbers_bob;
db << "SELECT numbers from person where name = ?;" << "bob" >> numbers_bob;

db << "SELECT numbers from person where name = ?;" << "sara" >> [](vector<double> numbers_sara){
    for(auto e : numbers_sara) cout << e << ' '; cout << endl;
};
```

NULL values
----
If you have databases where some rows may be null, you can use `std::unique_ptr<T>` to retain the NULL values between C++ variables and the database.

```c++
db << "CREATE TABLE tbl (id integer,age integer, name string, img blob);";
db << "INSERT INTO tbl VALUES (?, ?, ?, ?);" << 1 << 24 << "bob" << vector<int> { 1, 2 , 3};
unique_ptr<string> ptr_null; // you can even bind empty unique_ptr<T>
db << "INSERT INTO tbl VALUES (?, ?, ?, ?);" << 2 << nullptr << ptr_null << nullptr;

db << "select age,name,img from tbl where id = 1"
		>> [](unique_ptr<int> age_p, unique_ptr<string> name_p, unique_ptr<vector<int>> img_p) {
			if(age_p == nullptr || name_p == nullptr || img_p == nullptr) {
				cerr << "ERROR: values should not be null" << std::endl;
			}

			cout << "age:" << *age_p << " name:" << *name_p << " img:";
			for(auto i : *img_p) cout << i << ","; cout << endl;
		};

db << "select age,name,img from tbl where id = 2"
		>> [](unique_ptr<int> age_p, unique_ptr<string> name_p, unique_ptr<vector<int>> img_p) {
			if(age_p != nullptr || name_p != nullptr || img_p != nullptr) {
				cerr << "ERROR: values should be nullptr" << std::endl;
				exit(EXIT_FAILURE);
			}

			cout << "OK all three values are nullptr" << endl;
		};
```

SQLCipher
----

We have native support for [SQLCipher](https://www.zetetic.net/sqlcipher/).
If you want to use encrypted databases, include the `sqlite_moder_cpp/sqlcipher.h` header.
Then create a `sqlcipher_database` instead.

```c++
#include<iostream>
#include <sqlite_modern_cpp/sqlcipher.h>
using namespace sqlite;
using namespace std;

int main() {
   try {
      // creates a database file 'dbfile.db' if it does not exists with password 'secret'
      sqlcipher_config config;
      config.key = secret;
      sqlcipher_database db("dbfile.db", config);

      // executes the query and creates a 'user' table
      db <<
         "create table if not exists user ("
         "   _id integer primary key autoincrement not null,"
         "   age int,"
         "   name text,"
         "   weight real"
         ");";

      // More queries ...
      db.rekey("new_secret"); // Change the password of the already encrypted database.

      // Even more queries ..
   }
   catch (exception& e) { cout << e.what() << endl; }
}
```

NULL values (C++17)
----
You can use `std::optional<T>` as an alternative for `std::unique_ptr<T>` to work with NULL values.

```c++
#include <sqlite_modern_cpp.h>

struct User {
   long long _id;
   std::optional<int> age;
   std::optional<string> name;
   std::optional<real> weight;
};

int main() {
   User user;
   user.name = "bob";

   // Same database as above
   database db("dbfile.db");

   // Here, age and weight will be inserted as NULL in the database.
   db << "insert into user (age,name,weight) values (?,?,?);"
      << user.age
      << user.name
      << user.weight;
   user._id = db.last_insert_rowid();

   // Here, the User instance will retain the NULL value(s) from the database.
   db << "select _id,age,name,weight from user where age > ? ;"
      << 18
      >> [&](long long id,
         std::optional<int> age,
         std::optional<string> name
         std::optional<real> weight) {

      cout << "id=" << _id
         << " age = " << (age ? to_string(*age) ? string("NULL"))
         << " name = " << (name ? *name : string("NULL"))
         << " weight = " << (weight ? to_string(*weight) : string(NULL))
         << endl;
   };
}
```

If you do not have C++17 support, you can use boost optional instead by defining `_MODERN_SQLITE_BOOST_OPTIONAL_SUPPORT` before importing the `sqlite_modern_cpp` header.

If the optional library is not available, the experimental/optional one will be used instead.

**Note: boost support is deprecated and will be removed in future versions.**

Variant type support (C++17)
----
If your columns may have flexible types, you can use C++17's `std::variant` to extract the value.

```c++
db << "CREATE TABLE tbl (id integer, data);";
db << "INSERT INTO tbl VALUES (?, ?);" << 1 << vector<int> { 1, 2, 3};
db << "INSERT INTO tbl VALUES (?, ?);" << 2 << 2.5;

db << "select data from tbl where id = 1"
		>> [](std::variant<vector<int>, double> data) {
			if(data.index() != 1) {
				cerr << "ERROR: we expected a blob" << std::endl;
			}

			for(auto i : get<vector<int>>(data)) cout << i << ","; cout << endl;
		};

db << "select data from tbl where id = 2"
		>> [](std::variant<vector<int>, double> data) {
			if(data.index() != 2) {
				cerr << "ERROR: we expected a real number" << std::endl;
			}

			cout << get<double>(data) << endl;
		};
```

If you read a specific type and this type does not match the actual type in the SQlite database, yor data will be converted.
This does not happen if you use a `variant`.
If the `variant` does an alternative of the same value type, an `mismatch` exception will be thrown.
The value types are NULL, integer, real number, text and BLOB.
To support all possible values, you can use `variant<nullptr_t, sqlite_int64, double, string, vector<char>`.

Errors
----

On error, the library throws an error class indicating the type of error. The error classes are derived from the SQLITE3 error names, so if the error code is SQLITE_CONSTRAINT, the error class thrown is sqlite::errors::constraint. SQLite3 extended error names are supported too. So there is e.g. a class sqlite::errors::constraint_primarykey derived from sqlite::errors::constraint. Note that all errors are derived from sqlite::sqlite_exception and that itself is derived from std::runtime_exception.
sqlite::sqlite_exception has a `get_code()` member function to get the SQLITE3 error code or `get_extended_code()` to get the extended error code.
Additionally you can use `get_sql()` to see the SQL statement leading to the error.

```c++
database db(":memory:");
db << "create table person (id integer primary key not null, name text);";

try {
   db << "insert into person (id, name) values (?,?)" << 1 << "jack";
   // inserting again to produce error
   db << "insert into person (id, name) values (?,?)" << 1 << "jack";
}
/* if you are trying to catch all sqlite related exceptions
 * make sure to catch them by reference */
catch (sqlite_exception& e) {
   cerr  << e.get_code() << ": " << e.what() << " during "
         << e.get_sql() << endl;
}
/* you can catch specific exceptions as well,
   catch(sqlite::errors::constraint e) {  } */
/* and even more specific exceptions
   catch(sqlite::errors::constraint_primarykey e) {  } */
```

You can also register a error logging function with `sqlite::error_log`.
The `<sqlite_modern_cpp/log.h>` header has to be included to make this function available.
The call to `sqlite::error_log` has to be the first call to any `sqlite_modern_cpp` function by your program.

```c++
error_log(
   [&](sqlite_exception& e) {
      cerr  << e.get_code() << ": " << e.what() << endl;
   },
   [&](errors::misuse& e) {
      /* You can behave differently to specific errors */
   }
);
database db(":memory:");
db << "create table person (id integer primary key not null, name text);";

try {
   db << "insert into person (id, name) values (?,?)" << 1 << "jack";
   // inserting again to produce error
   db << "insert into person (id, name) values (?,?)" << 1 << "jack";
}
catch (sqlite_exception& e) {}
```

Custom SQL functions
----

To extend SQLite with custom functions, you just implement them in C++:

```c++
database db(":memory:");
db.define("tgamma", [](double i) {return std::tgamma(i);});
db << "CREATE TABLE numbers (number INTEGER);";

for(auto i=0; i!=10; ++i)
   db << "INSERT INTO numbers VALUES (?);" << i;

db << "SELECT number, tgamma(number+1) FROM numbers;" >> [](double number, double factorial) {
   cout << number << "! = " << factorial << '\n';
};
```

NDK support
----
Just Make sure you are using the full path of your database file :
`sqlite::database db("/data/data/com.your.package/dbfile.db")`.

Building and Installing
----

The usual way works for installing:

```bash
./configure && make && sudo make install

```

Note, there's nothing to make, so you there's no need to run configure and you can simply point your compiler at the hdr/ directory.

Breaking Changes
----
See breaking changes documented in each [Release](https://github.com/aminroosta/sqlite_modern_cpp/releases).

Package managers
----
Pull requests are welcome :wink:
- [AUR](https://aur.archlinux.org/packages/sqlite_modern_cpp/) Arch Linux
  - maintainer [Nissar Chababy](https://github.com/funilrys)
- Nuget (TODO [nuget.org](https://www.nuget.org/))
- Conan (TODO [conan.io](https://conan.io/))
- [vcpkg](https://github.com/Microsoft/vcpkg)

## License

MIT license - [http://www.opensource.org/licenses/mit-license.php](http://www.opensource.org/licenses/mit-license.php)