113 lines
2.9 KiB
Markdown
113 lines
2.9 KiB
Markdown
# JS Filter
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轻量、易读、可解析、可执行的类 SQL 过滤语法，用于 JavaScript 数组过滤。
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## 语法特性
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- **WHERE**: 条件过滤
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- **ORDER BY**: 排序
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- **LIMIT**: 限制结果数量
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- **操作符**: `=`, `!=`, `>`, `<`, `>=`, `<=`, `IN`, `CONTAINS`, `LIKE`, `NOT LIKE`, `IS NULL`, `IS NOT NULL`
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- **逻辑**: `AND`, `OR`
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## 语法示例
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```javascript
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// 基础过滤
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filter(users, "WHERE metadata.type = 'user'");
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// 多条件
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filter(users, "WHERE metadata.tags CONTAINS 'premium' AND metadata.region = 'beijing'");
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// 排序
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filter(users, "WHERE metadata.type = 'user' ORDER BY metadata.created_at DESC");
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// 限制数量
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filter(users, "WHERE metadata.type = 'user' ORDER BY metadata.created_at DESC LIMIT 10");
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// IN 操作
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filter(users, "WHERE metadata.region IN ['beijing', 'shanghai']");
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// LIKE 操作 (支持 % 匹配任意字符，_ 匹配单个字符)
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filter(products, "WHERE name LIKE '%Apple%'");
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filter(products, "WHERE name LIKE 'Apple%'");
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filter(products, "WHERE name LIKE '%Phone'");
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// NOT LIKE 操作 (排除匹配模式的项)
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filter(products, "WHERE name NOT LIKE '%Apple%'");
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// IS NULL 操作 (匹配 null 或 undefined 的值)
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filter(users, "WHERE email IS NULL");
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// IS NOT NULL 操作 (匹配非 null 且非 undefined 的值)
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filter(users, "WHERE email IS NOT NULL");
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```
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## 使用方法
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```javascript
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import { filter } from '@kevisual/js-filter';
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const users = [
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{
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metadata: {
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tags: ['premium', 'active'],
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type: 'user',
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region: 'beijing',
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created_at: '2024-03-15T10:00:00Z',
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},
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},
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{
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metadata: {
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tags: ['free'],
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type: 'admin',
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region: 'shanghai',
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created_at: '2024-01-10T09:00:00Z',
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},
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},
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{
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metadata: {
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tags: ['enterprise', 'premium'],
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type: 'user',
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region: 'guangzhou',
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created_at: '2024-04-05T12:00:00Z',
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},
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},
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];
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// 查找 premium 用户
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const premiumUsers = filter(users, "WHERE metadata.tags CONTAINS 'premium'");
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// 查找北京的用户，按创建时间倒序
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const beijingUsers = filter(users, "WHERE metadata.region = 'beijing' ORDER BY metadata.created_at DESC");
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```
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## 新增操作符说明
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### NOT LIKE
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排除匹配指定模式的数据项。
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```javascript
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// 查找不包含 "Apple" 的产品
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const nonAppleProducts = filter(products, "WHERE name NOT LIKE '%Apple%'");
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```
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### IS NULL / IS NOT NULL
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检查字段值是否为 `null` 或 `undefined`。
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```javascript
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const usersWithNullEmail = [
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{ name: 'Alice', email: 'alice@example.com', age: 25 },
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{ name: 'Bob', email: null, age: 30 },
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{ name: 'Charlie', email: undefined, age: 35 },
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];
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// 查找 email 为 null 或 undefined 的用户
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const usersWithoutEmail = filter(usersWithNullEmail, "WHERE email IS NULL");
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// 查找 email 不为 null 且不为 undefined 的用户
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const usersWithEmail = filter(usersWithNullEmail, "WHERE email IS NOT NULL");
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```
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**注意**: `IS NULL` 和 `IS NOT NULL` 会同时检查 JavaScript 的 `null` 和 `undefined` 值。
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