rsqlite

此库是一个无开销、高效的 sqlite C API 包装器。

// creates a database file 'dbfile.db' if it does not exists.
let database = Database::open("dbfile.db")?;

// executes the query and creates a 'user' table
database.execute(r#"
   create table if not exists user (
      id integer primary key autoincrement not null,
      age int,
      name text,
      weight real
   );"#, ())?;

// inserts a new user record.
// binds the fields to '?' .
// note that only these types are allowed for bindings:
//     int32, i64, f64, &str, &[u8]
// use `&[u8]` to store blob data.
database.execute(
   "insert into user(age, name, weight) values(?, ?, ?)",
   (29, "amin", 69.5)
)?;
let name = String::from("negar");
database.execute(
   "insert into user(age, name, weight) values(?, ?, ?)",
   (26, name.as_str(), 61.0)
)?;


// slects from user table on a condition ( age > 27 ),
// and executes the closure for each row returned.
database.for_each(
    "select name, age, weight from user where age > ?", (27),
    |name: String, age: i32, weight: f64| {
        dbg!(name, age, weight);
    }
)?;

// selects the count(*) from user table
// you can extract a single culumn single row result to:
// i32, i64, f64, String, Box<[u8]>
let count: i32 = database.collect("select count(*) from user", ())?;

// you can also extract single row with multiple columns
let amin: (i32, String, f64) = database.collect(
    "select age, name, weight from user where name = ?", ("amin")
)?;

// this also works, the returned value will be automatically converted to String
let str_count: String = database.collect("select count(*) from user", ())?;

额外标志

你可以向 SQLite 传递额外的打开标志

[dependencies]
sqlite3-sys = "*"

use rsqlite::{ffi, Database};

let flags = ffi::SQLITE_READONLY;
let database = Database::open_with_flags("dbfile.db", flags)?;

// now you can only read from the database
let n: i32 = database.collect(
    "select a from table where something >= ?", (1))?;

预处理语句

可以保留和重用语句，这会保持查询计划，如果语句被重用，可能会显著提高性能。

let mut statement = database.prepare("select age from user where age > ?")?;
// Database methods are simply implemented in terms of statements.
statement.for_each((27), |age: i32| {
    dbg!(age);
})?;

let age: i32 = database.prepare("select count(*) from user where age > ? limit 1")?
                       .collect((200))?;

NULL 值

如果你有可空的列，你可以使用 Option<T> 来传递和收集值。

// use `None` to insert NULL values
database.execute("insert into user(name, age) values (?,?)", (None::<&str>, 20))?;

// use Option<T> to collect them back
let (name, age) : (Option<String>, i32) =
                      database.collect("select name, age from user limit 1", ())?;
assert!((name, age) == (None, 20));

// an empty result set, would also be treated as None
let name : Option<String> = database.collect("select name from user where age = ?", (200))?;
assert!(name == None);

类型转换

sqlite 中的隐式类型转换遵循以下表格：例如，如果你收集一个 NULL 列作为 i32，你将得到 0。

事务

你可以使用 begin、commit 和 rollback 命令来使用事务。

database.execute("begin", ())?;    // begin a transaction ...
let mut statement = database.prepare("insert into user(name, age) values (?, ?)")?;
// insert 10 users using a prepared statement
for age in 0..10 {
  let name = format!("user-{}", age);
  statement.execute((name.as_str(), age))?;
}
database.execute("commit", ())?;   // commit all the changes

database.execute("begin", ())?;    // begin another transaction ...
database.execute("delete from user where age > ?", (3))?;
database.execute("rollback", ())?; // cancel this transaction

let sum_age : i32 = database.collect("select sum(age) from user", ())?;
assert!(sum_age == 45);

Blob

使用 &[u8] 来存储，使用 Box<[u8]> 来检索 blob 数据。

database.execute("create table user (name TEXT, numbers BLOB)", ())?;

let numbers = vec![1, 1, 2, 3, 5];
database.execute("insert into user values (?, ?)", ("amin", numbers.as_slice()))?;
let stored_numbers : Box<[u8]> =
         database.collect("select numbers from user where name = ?", ("amin"))?;
assert!(numbers.as_slice() == stored_numbers.as_ref());