WCF 4: Passing Empty parameters on a GET request

Question

I'm creating an API which will just use a get request to return some search results from the database, I'm trying to make it so that optional parameters can be passed (easy with WCF) but also so that if parameters are specfied in the query string as long as they are empty they will be ignored by the service.

However if you have the a query string with empty parameters it will return a bad request (400) by the server e.g.

Using a end-user point of your choice pass the following querystring

http://www.exampleservice.com/basic/?apiKey=1234&noOfResults=3&maxSalary=&minSalary=&ouId=0&keywords=Web+Developer

Note that maxSalary and minSalary are not passing values

You then have the following WCF service:

[OperationContract]
[WebGet(UriTemplate = "basic/?apiKey={apiKey}&noOfResults={noOfResults}&maxSalary={maxSalary}&minSalary={minSalary}&ouId={ouId}&keywords={keywords}", BodyStyle = WebMessageBodyStyle.Bare)]
        public List<SearchResultsDto> BasicSearch(string keywords, string apiKey, int noOfResults, int maxSalary, int minSalary, int ouId)
    {
          //Do some service stuff
    }

This will cause a 400 error, please can someone explain how you pass empty parameters across to a WCF service or is this just not possible?

score 2 · Accepted Answer · edited May 23 '17 at 10:33

Currently passing null or an empty parameter is not supported in WCF, the main solution to this problem is to override the querystringconverter which handles the url as it comes through the pipe but before it reaches the operation contract.

An excellent example of implmenting an extension of the querystringconverter is found here:

In the WCF web programming model, how can one write an operation contract with an array of query string parameters (i.e. with the same name)?

HOWEVER sadly there is a bug in WCF 4 where you cannot override the querystringconverter, this has been addressed by Microsoft and will be fixed in the SP1 release coming this year.

Until then there is no clean way to deal with this situation other than to handle the exception and return a status code of 400 (bad request) - good documentation of the api should handle this in the interim.

score 0 · Answer 2 · answered Jan 25 '11 at 12:39

0

Is it just the integers giving you trouble? Maybe you can try making them nullable?

int? MaxSalary

hope this helps

answered Jan 25 '11 at 12:39

Syg

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4
17

nullable types are not supported out of the box with WCF 4 and the querystringconverter cannot be overloaded at present. - nice answer though, with SP1 of WCF 4 this would have worked – Jay Feb 03 '11 at 12:07
Ah thanx for that, everyday is a schoolday ;-). In response to your other question: is querystring converter the only hook in the pipeline you have to change it? Wouldn't it be possible to remove the empty parameters in the OnBeginRequest event or something? – Syg Feb 11 '11 at 08:46

score 0 · Answer 3 · answered Jan 25 '11 at 14:02

0

You could send in "-1", and treat that in your business logic as not sent.

answered Jan 25 '11 at 14:02

Shiraz Bhaiji

64,065
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this is bad practice as it involves passing in false information to represent a different action i.e. making something resemble nothing. e.g. what if in the future you wanted to pass -1, this would be completely miss-interpreted. – Jay Feb 03 '11 at 12:06

humblelistener · Answer 4 · 2011-01-26T15:50:53.023

It can be handled in multiple ways. Since you are talking about a REST service that can have optional parameters, my suggestion will be do the something like this.

Create a DataObject that will be accepeted as parameter to this method.

[ServiceContract]
public interface IService1    
{
    [OperationContract]
    [WebGet(RequestFormat=WebMessageFormat.Json)]
    RequestObject BasicSearch(RequestObject apiKey);
}

public class Service1 : IService1
{
    public RequestObject BasicSearch(RequestObject obj)
    {
        //Do some service stuff

        return obj;
    }
}

[DataContract]
public class RequestObject
{      

    [DataMember]
    public string Keywords {get; set;}

    [DataMember]
    public string ApiKey {get; set;}

    [DataMember]
    public int NoOfResults { get; set; }

}

Advantages (am going to be short, ping me back for details)

No change in service signature contract does not change
you will get the flexibility of have null parameters
you can always extend the number of parameters without any impact to existing services

below is the sample input and output from fiddler note: in the request part i havent passed anything to NumberOfResults intentionally to prove Fiddler screen shot with sample request and response

WCF 4: Passing Empty parameters on a GET request

4 Answers4