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635616842c
The 'static bound was there to prevent callers from being able to save off the `SqliteRow` handles passed into the closure. This PR changes the closure to take `&SqliteRow`s instead, which provides the same feature without restricting the output of the closure.
105 lines
3.6 KiB
Markdown
105 lines
3.6 KiB
Markdown
# Rusqlite
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[](https://travis-ci.org/jgallagher/rusqlite)
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Rusqlite is an ergonomic wrapper for using SQLite from Rust. It attempts to expose
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an interface similar to [rust-postgres](https://github.com/sfackler/rust-postgres). View the full
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[API documentation](http://jgallagher.github.io/rusqlite/rusqlite/index.html).
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```rust
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extern crate rusqlite;
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extern crate time;
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use time::Timespec;
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use rusqlite::SqliteConnection;
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#[derive(Debug)]
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struct Person {
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id: i32,
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name: String,
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time_created: Timespec,
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data: Option<Vec<u8>>
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}
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fn main() {
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let conn = SqliteConnection::open_in_memory().unwrap();
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conn.execute("CREATE TABLE person (
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id INTEGER PRIMARY KEY,
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name TEXT NOT NULL,
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time_created TEXT NOT NULL,
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data BLOB
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)", &[]).unwrap();
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let me = Person {
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id: 0,
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name: "Steven".to_string(),
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time_created: time::get_time(),
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data: None
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};
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conn.execute("INSERT INTO person (name, time_created, data)
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VALUES ($1, $2, $3)",
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&[&me.name, &me.time_created, &me.data]).unwrap();
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let mut stmt = conn.prepare("SELECT id, name, time_created, data FROM person").unwrap();
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let mut person_iter = stmt.query_map(&[], |row| {
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Person {
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id: row.get(0),
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name: row.get(1),
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time_created: row.get(2),
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data: row.get(3)
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}
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}).unwrap();
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for person in person_iter {
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println!("Found person {:?}", person.unwrap());
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}
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}
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```
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### Design of SqliteRows and SqliteRow
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To retrieve the result rows from a query, SQLite requires you to call
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[sqlite3_step()](https://www.sqlite.org/c3ref/step.html) on a prepared statement. You can only
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retrieve the values of the "current" row. From the Rust point of view, this means that each row
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is only valid until the next row is fetched. [rust-sqlite3](https://github.com/dckc/rust-sqlite3)
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solves this the correct way with lifetimes. However, this means that the result rows do not
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satisfy the [Iterator](http://doc.rust-lang.org/std/iter/trait.Iterator.html) trait, which means
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you cannot (as easily) loop over the rows, or use many of the helpful Iterator methods like `map`
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and `filter`.
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Instead, Rusqlite's `SqliteRows` handle does conform to `Iterator`. It ensures safety by
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performing checks at runtime to ensure you do not try to retrieve the values of a "stale" row, and
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will panic if you do so. A specific example that will panic:
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```rust
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fn bad_function_will_panic(conn: &SqliteConnection) -> SqliteResult<i64> {
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let mut stmt = try!(conn.prepare("SELECT id FROM my_table"));
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let mut rows = try!(stmt.query(&[]));
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let row0 = try!(rows.next().unwrap());
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// row 0 is valid now...
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let row1 = try!(rows.next().unwrap());
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// row 0 is now STALE, and row 1 is valid
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let my_id = row0.get(0); // WILL PANIC because row 0 is stale
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Ok(my_id)
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}
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```
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There are other, less obvious things that may result in a panic as well, such as calling
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`collect()` on a `SqliteRows` and then trying to use the collected rows.
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Strongly consider using the method `query_map()` instead, if you can.
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`query_map()` returns an iterator over rows-mapped-to-some-type. This
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iterator does not have any of the above issues with panics due to attempting to
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access stale rows.
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## Author
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John Gallagher, johnkgallagher@gmail.com
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## License
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Rusqlite is available under the MIT license. See the LICENSE file for more info.
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