# 条件验证

### when 方法

```javascript
when(path, expect, chain)
```

* `path` 参数名
* `expect`  预期值
* `chain:` 验证链

```javascript
const rules = {
    type: acr.string().required().in([ 'personal', 'common' ]),
    age: acr.when('type', 'personal', () => {
        return acr.string().required().min(18);
    }),
};

// 抛出错误，age 必填
await acr.validate({
    type: 'personal',
}, rules);

// 抛出错误，age 不能小于 18
await acr.validate({
    type: 'personal',
    age: 16,
}, rules);

// 通过
await acr.validate({
    type: 'common',
    age: 16,
}, rules);
```

还可以使用 when 的重载方法来实现复杂条件的验证：

```javascript
when(expect, chain)
```

* `expect`  预期值
* `chain:` 验证链

```javascript
const rules = {
    type: acr.string().required().in([ 'personal', 'common' ]),
    age: acr.when((data, context) => {
        return data['type'] === 'persnoal';
    }, () => {
        return acr.string().required().min(18);
    }),
};
```

### other 方法

other 方法只接受一个闭包作为参数，闭包返回值为一个验证链。从逻辑上来说，other 包含 when 没有包含的所有可能，因此，无论声明顺序是怎样，other 总是在所有条件之后执行，并且多次调用 other 只有最后一次有效。

```javascript
const rules = {
    type: acr.string().required().in([ 'personal', 'common' ]),
    age: acr.when('type', 'personal', () => {
        return acr.number().required().min(18);
    }).other(() => {
        return acr.string().equal('');
    }),
};

// 抛出错误，age 不等于 '空字符串'
await acr.validate({
    type: 'common',
    age: 16,
}, rules);
```

### 多条件验证

在 when 方法后面，可以连接多个 when 方法，来实现更加复杂的条件验证。

```javascript
const rules = {
    type: acr.string().required().in([ 'personal', 'common' ]),
    age: acr.when('type', 'personal', () => {
        return acr.number().required().min(18);
    }).when('type', 'common', () => {
        return acr.string().equal('16');
    }),
};
```

### 多个参数联合验证

一个参数值的匹配，可以满足大多数情况的需求，针对一些极端条件，第一个参数可以提供闭包，返回一个 boolean 值来确定是否满足条件。

```javascript
const rules = {
    type: acr.string().required().in([ 'personal', 'common' ]),
    gender: acr.string().required().in([ 'male', 'female' ]),
    age: acr.when((data, context) => {
        return data['type'] === 'personal' && data['gender'] === 'male';
    }, () => {
        return acr.number().required().min(18);
    }),
}
```

### 异步条件

当第一个参数为闭包时，支持使用异步方法来判断是否符合条件。

```javascript
const rules = {
    gender: acr.string().required().in([ 'male', 'female' ]),
    age: acr.when(async (data, context) => {
        return await Promise.resolve(data['gender'] === 'male');
    }, () => {
        return acr.number().required().min(18);
    }),
}
```


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