Optional Parameters in Web Api Attribute Routing

Question

I want to handle POST of the following API-Call    v1 location deviceid appid  Additional Parameter are coming from the Post-Body   This all works fine for me  Now I wnat to extend my code by allowing  deviceid  and or  appid  and or BodyData to be null    v1 location deviceid  v1 location appid  v1 location    These 3 URLs should responded by the same route   My first approach  BodyData required     Route  v1 location  deviceid   appid    Name    AddNewLocation    public location fromuser Post string deviceid   null  string appid   null   FromBody  location fromuser BodyData        return repository AddNewLocation deviceid  appid  BodyData       This does not work and returns a compile error       optional Parameters must be at the end    Next try    Route  v1 location  deviceid   appid    Name    AddNewLocation    public location fromuser Post  FromBody  location fromuser BodyData  string deviceid   null  string appid   null    Now my function AddNewLocation   get always an BodyData null - even if the call send the Body   Finally I set all 3 Parameter optional    Route  v1 location  deviceid   appid    Name    AddNewLocation    public location fromuser Post string deviceid   null  string appid   null   FromBody location fromuser BodyData   null    Don  t work       Optional parameter BodyData is not supported by FormatterParameterBinding    Why do I want a solution with optional Parameters  My Controller handles just the  adding of a new Location  via a POST   I want to send on wrong data my own exceptions or error messages  Even if the call has missing values  In this case I want to be able to decide to throw an exception or Setting Defaults by my code

User · Answer

Another info  If you want use a Route Constraint  imagine that you want force that parameter has int datatype  then you need use this syntax    Route  v1 location    deviceOrAppid int       Name    AddNewLocation      The   character is put always before the last   character  For more information see  Optional URI Parameters and Default Values

User · Answer

For an incoming request like  v1 location 1234  as you can imagine it would be difficult for Web API to automatically figure out if the value of the segment corresponding to  1234  is related to appid and not to deviceid   I think you should change your route template to be like  Route  v1 location  deviceOrAppid     Name    AddNewLocation    and then parse the deiveOrAppid to figure out the type of id     Also you need to make the segments in the route template itself optional otherwise the segments are considered as required  Note the   character in this case  For example   Route  v1 location  deviceOrAppid     Name    AddNewLocation

User · Answer

Converting my comment into an answer to complement  Kiran Chala s answer as it seems helpful for the audiences-  When we mark a parameter as optional in the action uri using   character then we must provide default values to the parameters in the method signature as shown below    MyMethod string name    someDefaultValue   int  Id   null

[c#] Optional Parameters in Web Api Attribute Routing

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