mirror of https://github.com/sunface/rust-course
sunface
3 years ago
parent
2d43a8e4d4
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52d0c47375
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# Postgres
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### 在数据库中创建表格
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我们通过 [postgres](https://docs.rs/postgres/0.17.2/postgres/) 来操作数据库。下面的例子有一个前提：数据库 `library` 已经存在，其中用户名和密码都是 `postgres`。
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```rust,editable
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use postgres::{Client, NoTls, Error};
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fn main() -> Result<(), Error> {
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// 连接到数据库 library
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let mut client = Client::connect("postgresql://postgres:postgres@localhost/library", NoTls)?;
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client.batch_execute("
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CREATE TABLE IF NOT EXISTS author (
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id SERIAL PRIMARY KEY,
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name VARCHAR NOT NULL,
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country VARCHAR NOT NULL
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)
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")?;
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client.batch_execute("
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CREATE TABLE IF NOT EXISTS book (
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id SERIAL PRIMARY KEY,
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title VARCHAR NOT NULL,
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author_id INTEGER NOT NULL REFERENCES author
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)
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")?;
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Ok(())
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}
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```
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### 插入和查询
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```rust,editable
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use postgres::{Client, NoTls, Error};
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use std::collections::HashMap;
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struct Author {
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_id: i32,
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name: String,
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country: String
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}
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fn main() -> Result<(), Error> {
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let mut client = Client::connect("postgresql://postgres:postgres@localhost/library",
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NoTls)?;
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let mut authors = HashMap::new();
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authors.insert(String::from("Chinua Achebe"), "Nigeria");
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authors.insert(String::from("Rabindranath Tagore"), "India");
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authors.insert(String::from("Anita Nair"), "India");
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for (key, value) in &authors {
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let author = Author {
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_id: 0,
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name: key.to_string(),
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country: value.to_string()
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};
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// 插入数据
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client.execute(
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"INSERT INTO author (name, country) VALUES ($1, $2)",
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&[&author.name, &author.country],
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)?;
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}
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// 查询数据
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for row in client.query("SELECT id, name, country FROM author", &[])? {
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let author = Author {
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_id: row.get(0),
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name: row.get(1),
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country: row.get(2),
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};
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println!("Author {} is from {}", author.name, author.country);
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}
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Ok(())
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}
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```
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### 聚合数据
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下面代码将使用降序的方式列出 [Museum of Modern Art]() 数据库中的前 7999 名艺术家的国籍分布.
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```rust,editable
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use postgres::{Client, Error, NoTls};
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struct Nation {
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nationality: String,
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count: i64,
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}
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fn main() -> Result<(), Error> {
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let mut client = Client::connect(
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"postgresql://postgres:postgres@127.0.0.1/moma",
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NoTls,
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)?;
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for row in client.query
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("SELECT nationality, COUNT(nationality) AS count
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FROM artists GROUP BY nationality ORDER BY count DESC", &[])? {
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let (nationality, count) : (Option<String>, Option<i64>)
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= (row.get (0), row.get (1));
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if nationality.is_some () && count.is_some () {
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let nation = Nation{
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nationality: nationality.unwrap(),
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count: count.unwrap(),
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};
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println!("{} {}", nation.nationality, nation.count);
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}
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}
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Ok(())
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}
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```
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@ -1 +1,136 @@
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# SQLite
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### 创建 SQLite 数据库
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使用 `rusqlite` 可以创建 SQLite 数据库，[Connection::open](https://docs.rs/rusqlite/*/rusqlite/struct.Connection.html#method.open) 会尝试打开一个数据库，若不存在，则创建新的数据库。
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> 这里创建的 `cats.db` 数据库将被后面的例子所使用
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```rust,editable
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use rusqlite::{Connection, Result};
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use rusqlite::NO_PARAMS;
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fn main() -> Result<()> {
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let conn = Connection::open("cats.db")?;
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conn.execute(
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"create table if not exists cat_colors (
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id integer primary key,
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name text not null unique
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)",
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NO_PARAMS,
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)?;
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conn.execute(
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"create table if not exists cats (
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id integer primary key,
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name text not null,
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color_id integer not null references cat_colors(id)
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)",
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NO_PARAMS,
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)?;
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Ok(())
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}
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```
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### 插入和查询
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```rust,editable
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use rusqlite::NO_PARAMS;
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use rusqlite::{Connection, Result};
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use std::collections::HashMap;
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#[derive(Debug)]
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struct Cat {
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name: String,
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color: String,
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}
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fn main() -> Result<()> {
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// 打开第一个例子所创建的数据库
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let conn = Connection::open("cats.db")?;
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let mut cat_colors = HashMap::new();
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cat_colors.insert(String::from("Blue"), vec!["Tigger", "Sammy"]);
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cat_colors.insert(String::from("Black"), vec!["Oreo", "Biscuit"]);
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for (color, catnames) in &cat_colors {
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// 插入一条数据行
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conn.execute(
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"INSERT INTO cat_colors (name) values (?1)",
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&[&color.to_string()],
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)?;
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// 获取最近插入数据行的 id
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let last_id: String = conn.last_insert_rowid().to_string();
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for cat in catnames {
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conn.execute(
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"INSERT INTO cats (name, color_id) values (?1, ?2)",
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&[&cat.to_string(), &last_id],
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)?;
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}
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}
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let mut stmt = conn.prepare(
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"SELECT c.name, cc.name from cats c
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INNER JOIN cat_colors cc
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ON cc.id = c.color_id;",
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)?;
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let cats = stmt.query_map(NO_PARAMS, |row| {
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Ok(Cat {
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name: row.get(0)?,
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color: row.get(1)?,
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})
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})?;
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for cat in cats {
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println!("Found cat {:?}", cat);
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}
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Ok(())
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}
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```
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### 使用事务
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使用 [Connection::transaction](https://docs.rs/rusqlite/*/rusqlite/struct.Connection.html#method.transaction) 可以开始新的事务，若没有对事务进行显式地提交 [Transaction::commit](https://docs.rs/rusqlite/0.27.0/rusqlite/struct.Transaction.html#method.commit)，则会进行回滚。
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下面的例子中，`rolled_back_tx` 插入了重复的颜色名称，会发生回滚。
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```rust,editable
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use rusqlite::{Connection, Result, NO_PARAMS};
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fn main() -> Result<()> {
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// 打开第一个例子所创建的数据库
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let mut conn = Connection::open("cats.db")?;
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successful_tx(&mut conn)?;
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let res = rolled_back_tx(&mut conn);
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assert!(res.is_err());
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Ok(())
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}
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fn successful_tx(conn: &mut Connection) -> Result<()> {
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let tx = conn.transaction()?;
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tx.execute("delete from cat_colors", NO_PARAMS)?;
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tx.execute("insert into cat_colors (name) values (?1)", &[&"lavender"])?;
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tx.execute("insert into cat_colors (name) values (?1)", &[&"blue"])?;
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tx.commit()
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}
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fn rolled_back_tx(conn: &mut Connection) -> Result<()> {
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let tx = conn.transaction()?;
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tx.execute("delete from cat_colors", NO_PARAMS)?;
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tx.execute("insert into cat_colors (name) values (?1)", &[&"lavender"])?;
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tx.execute("insert into cat_colors (name) values (?1)", &[&"blue"])?;
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tx.execute("insert into cat_colors (name) values (?1)", &[&"lavender"])?;
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tx.commit()
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}
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```
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