mysql_orm

A C++ ORM for MySQL, inspired by sqlite_orm.

mysql_orm manages your queries to a MySQL database with an intuitive syntax and as much type-checking as possible at compile-time (hence reducing risks that a query is ill-formed).

Consider the following structure:

struct Record
{
  uint32_t id;
  int i;
  std::string s;
};

We can create a table from this structure the following way:

auto table_records = make_table("records",
                                make_column<&Record::id>("id"),
                                make_column<&Record::i>("i"),
                                make_column<&Record::s>("s"));

mysql_orm automatically deduces the types of the fields and the one of the structure (which we call the model). If the fields do not refer to the same model, an error is raised at compile-time.

We can now make a database connection from the table:

auto connection = mysql_orm::Connection("localhost", 3306, "username", "password", "database");
auto database = make_database(connection, table_records);

Any number of tables may be supplied when constructing a database. Any model whose table is given to the database may be used when performing a query with the database object. Note that all tables must refer to distinct models.

Performing queries

A SELECT query on a model is written the following way:

std::vector<Records> records = database.getAll<Record>()();

The database automatically chooses the table for Record on which to perform the query. By default all fields are selected. Some fields only may be selected by giving as template arguments the pointer to the attributes to select:

std::vector<Records> records = database.getAll<&Record::id, &Record::s>()();

This is the same as:

SELECT `id`, `s` FROM `records`

Adding clauses

SQL clauses are chained using operator()s:

database.getAll<Record>()(Where{c<&Record::i>{} = 3})(Limit<1>{})();

is equivalent to:

SELECT * FROM `records` WHERE `records`.`i`=3 LIMIT 1

c and ref

In order to build conditions correctly for WHERE and assignments for SET, you need to user one of the c and ref classes.

c is templated on a pointer to an attribute. When put in an operation, it will be substituted by the column corresponding to the attribute. In the above example, c<&Record::i>{} was changed to records.i.

ref takes a reference to the variable it is given, as opposed to taking it by value.

Let us look at the following:

int i = 4;

auto query = database.getAll<Record>()(Where{c<&Record::i>{}=ref{i});
query();
i = 2;
query();

The first call to query translates to

SELECT * FROM `records` WHERE `records`.`i`=4

While the second translates to

SELECT * FROM `records` WHERE `records`.`i`=2

Had we written c<&Record::i>{}=i, both calls would have been evaluated with i=4.

Roadmap

• Joins.
• Constraints on multiple columns (UNIQUE(a, b)).