refactor: 统一数据库相关命名规范并优化单例实现

- 统一使用DB类型别名替换Database类型定义
- 将 db 中间件中获取数据库实例的函数名从 getDb 改为 getDB 以保持命名一致性。
- 重命名数据库相关函数和类型以使用一致的命名规范，并确保单例模式正确返回数据库实例。

apps/server/src/server/api/context.ts

@@ -1,4 +1,4 @@
-import type { Database } from '@/server/db'
+import type { DB } from '@/server/db'
 
 /**
  * 基础 Context - 所有请求都包含的上下文
@@ -11,7 +11,7 @@ export interface BaseContext {
  * 数据库 Context - 通过 db middleware 扩展
  */
 export interface DBContext extends BaseContext {
-  db: Database
+  db: DB
 }
 
 /**

apps/server/src/server/api/middlewares/db.middleware.ts

@@ -1,11 +1,11 @@
 import { os } from '@orpc/server'
-import { getDb } from '@/server/db'
+import { getDB } from '@/server/db'
 
 export const db = os.middleware(async ({ context, next }) => {
   return next({
     context: {
       ...context,
-      db: getDb(),
+      db: getDB(),
     },
   })
 })

apps/server/src/server/db/index.ts

@@ -2,7 +2,7 @@ import { drizzle } from 'drizzle-orm/postgres-js'
 import { env } from '@/env'
 import * as schema from '@/server/db/schema'
 
-export const createDb = () =>
+export const createDB = () =>
   drizzle({
     connection: {
       url: env.DATABASE_URL,
@@ -11,17 +11,17 @@ export const createDb = () =>
     schema,
   })
 
-export type Database = ReturnType<typeof createDb>
+export type DB = ReturnType<typeof createDB>
 
-export const getDb = (() => {
+export const getDB = (() => {
-  let db: Database | null = null
+  let db: DB | null = null
 
-  return (singleton = true): Database => {
+  return (singleton = true): DB => {
     if (!singleton) {
-      return createDb()
+      return createDB()
     }
 
-    db ??= createDb()
+    db ??= createDB()
     return db
   }
 })()