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<Nothing>
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;

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.

You can also use monadic error handling here:

using namespace sqlgen;

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

// sqlgen::Result<Nothing>
const auto result = sqlite::connect("database.db").and_then(query);

Example: Full Query Composition

using namespace sqlgen;

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

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

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. 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).value();

Notes

• The where clause is optional - if omitted, all records will be deleted
• The Result<Nothing> 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 results for other forms of error handling.
• "..."_c refers to the name of the column