Question

我有一些过滤操作

type FilterOp = 'Equals' | 'NotEquals' | 'Greater' | 'GreaterEqual' | 'Less' | 'LessEqual';
type ArrayFilterOp = 'In' | 'NotIn';
type StringFilterOp = 'StartsWith' | 'EndsWith' | 'Contains' | 'NotContains';
type DateFilterOp = 'DateIn' | 'DateNotIn'

这是我当前的过滤器定义

type GenericFilter<T> = {
    Property: string,
    Value: T,
    Operation: FilterOp | ArrayFilterOp | StringFilterOp | DateFilterOp
}

是否可以基于Operation参数确定T类型？例如，如果我的T是Date，那么打字稿将只允许DateFilterOp和FilterOp分配给Operation属性

let dateFilter: GenericFilter<Date> = {
    Property: "DateCreated",
    Value: new Date(),
    Operation: // now I can only set value from FilterOp or DateFilterOp
}

Answer 1

假设我正确理解了约束，则可以使用conditional types来表示它：

type Operation<T> =
  | FilterOp
  | (T extends Array<any> ? ArrayFilterOp : never)
  | (T extends string ? StringFilterOp : never)
  | (T extends Date ? DateFilterOp : never);

type GenericFilter<T> = {
  Property: string;
  Value: T;
  Operation: Operation<T>;
};

这将支持您陈述的用例：

let dateFilter: GenericFilter<Date> = {
  Property: "DateCreated",
  Value: new Date(),
  Operation: "DateIn"
};

以及使用辅助功能，因此您可以推断 T，而无需手动指定：

const asGenericFilter = <T>(filt: GenericFilter<T>) => filt;

let stringFilter = asGenericFilter({
  Property: "Name",
  Value: "Alice",
  Operation: "StartsWith" // hinted as Operation<string>
})

希望有所帮助；祝你好运！

Link to code

Answer 2

我设法通过OperationMap

实施了解决方案

type OperationMap<T> = 
    T extends Date
        ? (DateFilterOp | FilterOp)
        : T extends Array<any>
            ? ArrayFilterOp
            : T extends String
                ? FilterOp | StringFilterOp
    : FilterOp;

type GenericFilter<T> = {
    Property: string,
    Value: T,
    Operation: OperationMap<T>
}

从泛型参数类型确定Typescript属性联合

2 个答案: