读副本

当您的项目涉及一组读副本实例时，如果您需要一种便捷的方法来管理来自读副本的 SELECT 查询，以及在主实例上执行创建、删除和更新操作，您可以使用 Drizzle 中的 withReplicas() 函数。

PostgreSQL

MySQL

SQLite

SingleStore

import { sql } from 'drizzle-orm';
import { drizzle } from 'drizzle-orm/node-postgres';
import { boolean, jsonb, pgTable, serial, text, timestamp, withReplicas } from 'drizzle-orm/pg-core';

const usersTable = pgTable('users', {
	id: serial('id' as string).primaryKey(),
	name: text('name').notNull(),
	verified: boolean('verified').notNull().default(false),
	jsonb: jsonb('jsonb').$type<string[]>(),
	createdAt: timestamp('created_at', { withTimezone: true }).notNull().defaultNow(),
});

const primaryDb = drizzle("postgres://user:password@host:port/primary_db");
const read1 = drizzle("postgres://user:password@host:port/read_replica_1");
const read2 = drizzle("postgres://user:password@host:port/read_replica_2");

const db = withReplicas(primaryDb, [read1, read2]);

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";
import { boolean, mysqlTable, serial, text, withReplicas } from 'drizzle-orm/mysql-core';

const usersTable = mysqlTable('users', {
	id: serial('id' as string).primaryKey(),
	name: text('name').notNull(),
	verified: boolean('verified').notNull().default(false),
});

const primaryClient = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "primary_db",
})
const primaryDb = drizzle({ client: primaryClient });

const read1Client = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "read_1",
})
const read1 = drizzle({ client: read1Client });

const read2Client = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "read_2",
})
const read2 = drizzle({ client: read2Client });

const db = withReplicas(primaryDb, [read1, read2]);

import { sql } from 'drizzle-orm';
import { sqliteTable, int, text, withReplicas } from 'drizzle-orm/sqlite-core';
import { createClient } from '@libsql/client';
import { drizzle } from 'drizzle-orm/libsql';

const usersTable = sqliteTable('users', {
	id: int('id' as string).primaryKey(),
	name: text('name').notNull(),
});

const primaryDb = drizzle({ client: createClient({ url: 'DATABASE_URL', authToken: 'DATABASE_AUTH_TOKEN' }) });
const read1 = drizzle({ client: createClient({ url: 'DATABASE_URL', authToken: 'DATABASE_AUTH_TOKEN' }) });
const read2 = drizzle({ client: createClient({ url: 'DATABASE_URL', authToken: 'DATABASE_AUTH_TOKEN' }) });

const db = withReplicas(primaryDb, [read1, read2]);

import { drizzle } from "drizzle-orm/singlestore";
import mysql from "mysql2/promise";
import { boolean, singlestoreTable, serial, text, withReplicas } from 'drizzle-orm/singlestore-core';

const usersTable = singlestoreTable('users', {
	id: serial('id' as string).primaryKey(),
	name: text('name').notNull(),
	verified: boolean('verified').notNull().default(false),
});

const primaryClient = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "primary_db",
})
const primaryDb = drizzle({ client: primaryClient });

const read1Client = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "read_1",
})
const read1 = drizzle({ client: read1Client });

const read2Client = await mysql.createConnection({
  host: "host",
  user: "user",
  database: "read_2",
})
const read2 = drizzle({ client: read2Client });

const db = withReplicas(primaryDb, [read1, read2]);

您现在可以像以前一样使用 db 实例。Drizzle 将自动处理读副本和主实例之间的选择。

// Read from either the read1 connection or the read2 connection
await db.select().from(usersTable)

// Use the primary database for the delete operation
await db.delete(usersTable).where(eq(usersTable.id, 1))

您可以使用 $primary 键强制使用主实例，即使是读操作。

// read from primary
await db.$primary.select().from(usersTable);

使用 Drizzle，您还可以为选择读副本指定自定义逻辑。您可以采用加权决策或其他任何自定义选择方法来进行随机读副本选择。以下是一个选择读副本的自定义逻辑实现示例，其中第一个副本有 70% 的几率被选中，第二个副本有 30% 的几率被选中。

请记住，您可以为读副本实现任何类型的随机选择方法。

const db = withReplicas(primaryDb, [read1, read2], (replicas) => {
    const weight = [0.7, 0.3];
    let cumulativeProbability = 0;
    const rand = Math.random();

    for (const [i, replica] of replicas.entries()) {
      cumulativeProbability += weight[i]!;
      if (rand < cumulativeProbability) return replica;
    }
    return replicas[0]!
});

await db.select().from(usersTable)