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98 lines
2.2 KiB
Markdown
98 lines
2.2 KiB
Markdown
# `sqlgen::drop`
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The `sqlgen::drop` interface provides a type-safe way to drop tables from a SQL database. It supports the `if_exists` clause to handle cases where the table may not exist.
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## Usage
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### Basic Drop
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Drop a table:
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```cpp
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const auto conn = sqlgen::sqlite::connect("database.db");
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sqlgen::drop<Person>(conn).value();
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```
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This generates the following SQL:
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```sql
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DROP TABLE "Person";
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```
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Note that `conn` is actually a connection wrapped into an `sqlgen::Result<...>`.
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This means you can use monadic error handling and fit this into a single line:
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```cpp
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// sqlgen::Result<Ref<Connection>>
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const auto result = sqlgen::sqlite::connect("database.db").and_then(
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sqlgen::drop<Person>);
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```
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Please refer to the documentation on `sqlgen::Result<...>` for more information on error handling.
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### With `if_exists` clause
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Drop a table only if it exists:
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```cpp
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using namespace sqlgen;
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const auto query = drop<Person> | if_exists;
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query(conn).value();
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```
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This generates the following SQL:
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```sql
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DROP TABLE IF EXISTS "Person";
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```
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You can also use monadic error handling here:
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```cpp
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using namespace sqlgen;
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const auto query = drop<Person> | if_exists;
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// sqlgen::Result<Ref<Connection>>
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const auto result = sqlite::connect("database.db").and_then(query);
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```
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## Example: Full Query Composition
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```cpp
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using namespace sqlgen;
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const auto query = drop<Person> | if_exists;
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const auto result = query(conn);
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if (!result) {
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// Error handling
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}
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```
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This generates the following SQL:
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```sql
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DROP TABLE IF EXISTS "Person";
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```
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It is strongly recommended that you use `using namespace sqlgen`. However,
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if you do not want to do that, you can rewrite the example above as follows:
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```cpp
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const auto query = sqlgen::drop<Person> | sqlgen::if_exists;
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const auto result = query(conn);
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```
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## Notes
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- The `if_exists` clause is optional - if omitted, the query will fail if the table doesn't exist
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- 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.
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- The table name is derived from the struct name (e.g., `Person` becomes `"Person"` in SQL)
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