sqlgen/docs/delete_from.md

sqlgen::delete_from

The sqlgen::delete_from interface provides a type-safe way to delete records from a SQL database. It supports composable query building with where clauses to specify which records should be deleted.

Usage

Basic Delete

Delete all records from a table:

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

sqlgen::delete_from<Person>(conn).value();

This generates the following SQL:

DELETE FROM "Person";

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:

// sqlgen::Result<Ref<Connection>>
const auto result = sqlgen::sqlite::connect("database.db").and_then(
                        sqlgen::delete_from<Person>);

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

With where clause

Delete specific records using a where clause:

using namespace sqlgen;
using namespace sqlgen::literals;

const auto query = delete_from<Person> |
                   where("first_name"_c == "Hugo");

query(conn).value();

This generates the following SQL:

DELETE FROM "Person"
WHERE "first_name" = 'Hugo';

Note that "..."_c refers to the name of the column. If such a field does not exist on the struct Person, the code will fail to compile. "..."_c is defined in the namespace sqlgen::literals.

You can also use monadic error handling here:

using namespace sqlgen;
using namespace sqlgen::literals;

const auto query = delete_from<Person> |
                   where("first_name"_c == "Hugo");

// sqlgen::Result<Ref<Connection>>
const auto result = sqlite::connect("database.db").and_then(query);

Example: Full Query Composition

using namespace sqlgen;
using namespace sqlgen::literals;

const auto query = delete_from<Person> |
                   where("age"_c >= 18 and "last_name"_c == "Simpson");

const auto result = query(conn);

if (!result) {
    // Error handling
}

This generates the following SQL:

DELETE FROM "Person"
WHERE ("age" >= 18) AND ("last_name" = 'Simpson');

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

const auto query = sqlgen::delete_from<Person> |
                   sqlgen::where(sqlgen::col<"age"> >= 18 and sqlgen::col<"last_name"> == "Simpson");

const auto result = query(conn);

Notes

• The where clause is optional - if omitted, all records will be deleted
• The Result<Ref<Connection>> type provides error handling; use .value() to extract the result (will throw an exception if there's an error) or handle errors as needed or refer to the documentation on sqlgen::Result<...> for other forms of error handling.
• "..."_c refers to the name of the column