# Filters

Filters feature lets you create a custom decorators that will be used on the methods parameters like or .

# Example

This example show you, how you can implement a filter and decorator to use these, on a method Controller. In this case, we need to retrieve the body content from an Express.Request.

So to do that, you must create a class and annotate it with the decorator and in option, implement the interface:

import {Filter, IFilter, ParseService} from "@tsed/common";
import * as Express from "express";

@Filter()
export class CustomBodyParamFilter implements IFilter {

  constructor(private parseService: ParseService) {
  }

  transform(expression: string, request: Express.Request, response: Express.Response) {
    return this.parseService.eval(expression, request["body"]);
  }
}
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Then create the decorator. This decorator will be used on a controller method.

import {IParamOptions, ParamTypes, UseFilter} from "@tsed/common";
import {CustomBodyParamFilter} from "./CustomBodyParamFilter";

export function CustomBodyParams(options: IParamOptions<any> = {}): ParameterDecorator {
  const {expression, useType, useConverter = true, useValidation = true} = options;

  return UseFilter(CustomBodyParamFilter, {
    expression,
    useType,
    useConverter,
    useValidation,
    paramType: ParamTypes.BODY // for swagger
  });
}
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And finally you can use your custom filter on your controller/middleware:

import {Controller, Post} from "../../../../packages/common/src/mvc/decorators";
import {CustomBodyParams} from "./filter-decorator";


@Controller("/")
export class MyController {

  @Post("/")
  save(@CustomBodyParams({}) payload: any) {
    console.log(payload);
  }
}
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# UseFilter Options

allow you to register your custom decorator with few options as following:

  • paramType (ParamTypes): Parameter type like BODY, QUERY, PARAMS, etc...,
  • required (boolean, optional): Throw an error when if the value is undefined,
  • expression (string, optional): An expression to parse,
  • useConverter (boolean): Enable converterService to deserialize value,
  • useValidation (boolean): Enable ValidationService,
  • useType (boolean): Set explicitly the class/model used by the parameters.