`sqlgen::read`

The sqlgen::read interface provides a flexible and type-safe way to query data from a SQL database into C++ containers or ranges. It supports composable query building with where, order_by, and limit clauses.

Usage

Basic Read

Read all rows from a table into a container (e.g., std::vector<Person>):

const auto conn = sqlgen::sqlite::connect("database.db");

const auto people = sqlgen::read<std::vector<Person>>(conn).value();

Note that conn is actually a connection wrapped into an sqlgen::Result<...>. This means you can use monadic error handling and fit this into a single line:

const auto people = sqlgen::sqlite::connect("database.db").and_then(
                        sqlgen::read<std::vector<Person>>).value();

Please refer to the documentation on sqlgen::Result<...> for more information.

With `where` clause

Filter results using a where clause:

using namespace sqlgen;

const auto query = sqlgen::read<std::vector<Person>> |
                   where("age"_c < 18 and "first_name"_c != "Hugo");

const auto minors = query(conn).value();

Note that "..."_c refers to the name of the column. If such a field does not exists on the struct Person, the code will fail to compile.

You can also use monadic error handling here:

using namespace sqlgen;

const auto query = sqlgen::read<std::vector<Person>> |
                   where("age"_c < 18 and "first_name"_c != "Hugo");

const auto minors = sqlite::connect("database.db").and_then(query).value();

With `order_by` and `limit`

Sort and limit results:

using namespace sqlgen;

const auto query = sqlgen::read<std::vector<Person>> |
                   order_by("age"_c) |
                   limit(2);

const auto youngest_two = query(conn).value();

With ranges

Read results as a lazy range:

const auto people_range = sqlgen::read<sqlgen::Range<Person>>(conn).value();
for (const sqlgen::Result<Person>& person : people_range) {
    // process result 
}

Example: Full Query Composition

using namespace sqlgen;

const auto query = sqlgen::read<std::vector<Person>> |
                   where("age"_c >= 18) |
                   order_by("last_name"_c, "first_name"_c.desc()) |
                   limit(10);

const auto adults = query(conn).value();

It is strongly recommended that you use using namespace sqlgen. However, if you do not want to do that, you can rewrite the example above as follows:

const auto query = sqlgen::read<std::vector<Person>> |
                   sqlgen::where(sqlgen::col<"age"> >= 18) |
                   sqlgen::order_by(sqlgen::col<"last_name">, sqlgen::col<"first_name">.desc()) |
                   sqlgen::limit(10);

const auto adults = query(conn).value();

Notes

All query clauses (where, order_by, limit) are optional.
The Result<ContainerType> type provides error handling; use .value() to extract the result (will throw a exception if the results) or handle errors as needed. Refer to the
The sqlgen::Range<T> type allows for lazy iteration over results.
"..."_c refers to the name of the column.

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sqlgen::read