JSON deserializer cannot create & populate object

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Hello,

I've been wrangling with deserializing a certain json snippet into an object that deploys the IEnumerable interface so I can loop through its list and use some of its attributes as parameters in a SQL query.

I already received a few answers that didn't solve the problem. You can view them here:

c# - Error Deserializing JSON into IEnumerable<T> Object - Stack Overflow[^]

I will post an example of the json string, my classes to handle the deserialization, the error I'm receiving when I attempt to do so, and how the new object will be being used when it is correctly deserialized.

What I have tried:

//Json Example:

{
    	"ErrorCode":""
    	,"ErrorMessage":""
    	,"AppointmentReasonList":[
    		{
    			"ClassCode":"851"
    			,"ClassDescription":"newpat"
    			,"Active":true
    			,"IsPatientRelated":true
    			,"ReasonCodeList":[
    				{
    					"Code":"851"
    					,"Description":"Emergency New Patient Visit"
    					,"Duration":15
    					,"Active":true
    				}
    				,{
    					"Code":"BH NEW"
    					,"Description":"BH NEW"
    					,"Duration":15
    					,"Active":true
    				}
    							]
    		}
    		,{
    			"ClassCode":"ANE"
    			,"ClassDescription":"Anesthesia"
    			,"Active":true
    			,"IsPatientRelated":true
    			,"ReasonCodeList":[
    				{
    					"Code":"123456"
    					,"Description":"This is only a test"
    					,"Duration":15
    					,"Active":true
    				}
    								]
    		}					
    							]
    }

 //Classes to handle JSON structure

        public class AppointmentReasonResponse
        {
            public string ErrorCode { get; set; }
            public string ErrorMessage { get; set; }
            public AppointmentReasonList AppointmentReasonList { get; set; }
        }

        public class AppointmentReasonList : IEnumerable<AppointmentReason>
        {

            public List<AppointmentReason> AppointmentReasonLi { get; set; }

            IEnumerator<AppointmentReason> IEnumerable<AppointmentReason>.GetEnumerator()
            {
                foreach (AppointmentReason ApptReason in AppointmentReasonLi)
                {
                    yield return ApptReason;
                }
            }

            public IEnumerator<AppointmentReason> GetEnumerator()
            {
                return AppointmentReasonLi.GetEnumerator();
            }

            IEnumerator IEnumerable.GetEnumerator()
            {
                return this.GetEnumerator();
            }
        }

        public class AppointmentReason 
        {

            public string ClassCode { get; set; }
            public string ClassDescription { get; set; }
            public bool Active { get; set; }
            public bool IsPatientRelated { get; set; }
            public ReasonCodeList ReasonCodeList { get; set; }
        }

        public class ReasonCodeList : IEnumerable<ReasonCode>
        {
            public List<ReasonCode> ReasonCodeLi { get; set; }

            IEnumerator<ReasonCode> IEnumerable<ReasonCode>.GetEnumerator()
            {
                // Return the array object's IEnumerator.
                foreach (ReasonCode Reason in ReasonCodeLi)
                {
                    yield return Reason;
                }
            }

            public IEnumerator<ReasonCode> GetEnumerator()
            {
                // Return the array object's IEnumerator.
                return ReasonCodeLi.GetEnumerator();
            }

            IEnumerator IEnumerable.GetEnumerator()
            {
                // call the generic version of the method
                return this.GetEnumerator();
            }
        }

        public class ReasonCode
        {
            public string Code { get; set; }
            public string Description { get; set; }
            public int Duration { get; set; }
            public bool Active { get; set; }
        }

//use of resulting object

jarray = JsonConvert.DeserializeObject<AppointmentReasonResponse>(json);
        foreach (AppointmentReason ApptReason in jarray.AppointmentReasonList)
        {
            foreach (ReasonCode Reason in ApptReason)
            {
                AddInterfacePMReasonCode(PracticeID, Reason.Code, Reason.Description);
            }
        }

Here is the error I'm getting:

Quote:
{"Cannot create and populate list type AppointmentReasonList. Path 'AppointmentReasonList', line 1, position 59."}

Would love any help feedback you can provide.

Posted 27-Apr-18 11:12am

Member 13801974

Updated 28-Apr-18 10:11am

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Eric Lynch · Accepted Answer · 2018-04-28T10:12:00

You're biggest problems are with the AppointmentReasonList and ReasonCodeList classes. In your JSON document, these are represented as collections. However, since both classes simply implement IEnumerable{T}, there is no way the de-serializer can add elements to the collection.

Consider either inheriting directly from the List{T} class or implementing ICollection{T} or IList{T}.

In my experiments, both of these resolved the issue you note.

Separately, one of your foreach loops is not valid, AppointmentReason is not enumerable, you probably mean ApptReason.ReasonCodeList.

So, just to clarify, below are the recommended fixes. Each has been tested in VS 2017 (with the call to the missing AddInterfaceRMReasonCode commented out).

This is the recommended fix to the foreach loop:

C#

foreach (AppointmentReason ApptReason in jarray.AppointmentReasonList)
{
  foreach (ReasonCode Reason in ApptReason.ReasonCodeList)
  {
    AddInterfacePMReasonCode(PracticeID, Reason.Code, Reason.Description);
  }
}

This is the easiest fix to the problems with your classes:

C#

public class AppointmentReasonList : List<AppointmentReason>
{
}

public class ReasonCodeList : List<ReasonCode>
{
}

In case you were simply providing some code clips, and have a reason for not using the simplest fix, below is a fix that is closest to your original code:

C#

public class AppointmentReasonList : ICollection<AppointmentReason>
{
	public AppointmentReasonList()
	{
		AppointmentReasonLi = new List<AppointmentReason>();
	}

	public List<AppointmentReason> AppointmentReasonLi { get; set; }

	public int Count
	{
		get { return AppointmentReasonLi.Count; }
	}

	public bool IsReadOnly
	{
		get
		{
			return false;
		}
	}

	public void Add(AppointmentReason item)
	{
		AppointmentReasonLi.Add(item);
	}

	public void Clear()
	{
		AppointmentReasonLi.Clear();
	}

	public bool Contains(AppointmentReason item)
	{
		return AppointmentReasonLi.Contains(item);
	}

	public void CopyTo(AppointmentReason[] array, int arrayIndex)
	{
		AppointmentReasonLi.CopyTo(array, arrayIndex);
	}

	public IEnumerator<AppointmentReason> GetEnumerator()
	{
		return AppointmentReasonLi.GetEnumerator();
	}

	public bool Remove(AppointmentReason item)
	{
		return AppointmentReasonLi.Remove(item);
	}

	IEnumerator IEnumerable.GetEnumerator()
	{
		return GetEnumerator();
	}
}

public class ReasonCodeList : ICollection<ReasonCode>
{
	public ReasonCodeList()
	{
		ReasonCodeLi = new List<ReasonCode>();
	}

	public List<ReasonCode> ReasonCodeLi { get; set; }

	public int Count
	{
		get { return ReasonCodeLi.Count; }
	}

	public bool IsReadOnly
	{
		get
		{
			return false;
		}
	}

	public void Add(ReasonCode item)
	{
		ReasonCodeLi.Add(item);
	}

	public void Clear()
	{
		ReasonCodeLi.Clear();
	}

	public bool Contains(ReasonCode item)
	{
		return ReasonCodeLi.Contains(item);
	}


	public void CopyTo(ReasonCode[] array, int arrayIndex)
	{
		ReasonCodeLi.CopyTo(array, arrayIndex);
	}

	public IEnumerator<ReasonCode> GetEnumerator()
	{
		return ReasonCodeLi.GetEnumerator();
	}


	public bool Remove(ReasonCode item)
	{
		return ReasonCodeLi.Remove(item);
	}


	IEnumerator IEnumerable.GetEnumerator()
	{
		return GetEnumerator();
	}
}

Good luck, hope this helps.

-Eric.