Xml序列化无法在ASP.NET Web Api中按预期方式工作

Question

We have a Web API which uses a base class for all the models. Below is the structure

Base abstract class

[DataContract(Namespace = "")]
public abstract class Criteria
{
    protected Criteria()
    {
        Offset = 0;
        Limit = 250;
    }
    [DataMember(Name = "offset", Order = 97, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public int? Offset { get; set; }

    [DataMember(Name = "limit", Order = 98, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public int? Limit { get; set; }
}

This implements the base abstract class

[DataContract(Name = "insightCriteria", Namespace = "")]
public class InsightCriteria : Criteria
{
    [DataMember(Name = "geography", Order = 95, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    [JsonConverter(typeof(StringEnumConverter))]
    public InsightGeography Geography { get; set; }
}

Actual model which implements above class further

[DataContract(Name = "jobReportCriteria", Namespace = "")]
public class JobReportCriteria : InsightCriteria
{
    [DataMember(Name = "groupBy", Order = 1, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    [JsonConverter(typeof(StringEnumConverter))]
    public JobReportGroupings GroupBy { get; set; }

    [DataMember(Name = "timePeriod", Order = 2, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public TimePeriod TimePeriod { get; set; }

    [DataMember(Name = "queryString", Order = 3, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public string QueryString { get; set; }

    [DataMember(Name = "includeTotalClassifiedPostings", Order = 4, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public bool IncludeTotalClassifiedPostings { get; set; }

    [DataMember(Name = "includeTotalUnclassifiedPostings", Order = 5, EmitDefaultValue = false)]
    [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore)]
    public bool IncludeTotalUnclassifiedPostings { get; set; }
}

Issue

Now the problem is when using json serialization everything works fine I'm receiving values for offset and limit in the abstract class. But when using XML serialization the offset and limit is not getting populated.

Below is request I'm passing to api via Rest Client

<jobReportCriteria>
  <groupBy>State</groupBy>
  <timePeriod>
    <from>2014-02-06T00:00:00</from>
    <to>2014-05-06T00:00:00</to>
  </timePeriod>
  <queryString>[nationwide]: &quot; nationwide &quot;</queryString>
  <includeTotalClassifiedPostings>true</includeTotalClassifiedPostings>
  <includeTotalUnclassifiedPostings>true</includeTotalUnclassifiedPostings>
  <includeLastDataDate>true</includeLastDataDate>
  <offset>0</offset>
  <limit>25</limit>
</jobReportCriteria>

Strange behaviour

If i changed the order of the elements then the offset and limit are getting populated. below is request that is getting serialized correctly

<jobReportCriteria>
  <offset>0</offset>
  <limit>25</limit>
  <groupBy>State</groupBy>
  <timePeriod>
    <from>2014-02-06T00:00:00</from>
    <to>2014-05-06T00:00:00</to>
  </timePeriod>
  <queryString>[nationwide]: &quot; nationwide &quot;</queryString>
  <includeTotalClassifiedPostings>true</includeTotalClassifiedPostings>
  <includeTotalUnclassifiedPostings>true</includeTotalUnclassifiedPostings>
  <includeLastDataDate>true</includeLastDataDate>
</jobReportCriteria>

Putting offset and limit at the start somehow enables the serialization. The problem is i cant ask the client to frame the request in specific order.

Can someone let me know what exactly going on here?

Update:

On further analysis i came to know that order of the data members influence the Serialization but still i think i have ordered my members accordingly and given offset and limit values a maximum order so that it always comes below other parameters. but still it comes as null

Answer 1

The order in which DataContractSerializer requires elements to be encountered is spelled out here: Data Member Order :

The basic rules for data ordering include:

• If a data contract type is a part of an inheritance hierarchy, data members of its base types are always first in the order.

• Next in order are the current type's data members that do not have the Order property of the DataMemberAttribute attribute set, in alphabetical order.

• Next are any data members that have the Order property of the DataMemberAttribute attribute set. These are ordered by the value of the Order property first and then alphabetically if there is more than one member of a certain Order value. Order values may be skipped.

Alphabetical order is established by calling the CompareOrdinal method.

Ie, base class data members (ie offset and limit of Criteria ) must needs appear before derived class data members.

So, here are some possibilities to work around this rule:

1. Modify your class design and flatten your class hierarchy. Obviously not ideal, but you could do it by replacing a class hierarchy with an interface hierarchy implemented by flat classes.

2. Use a data contract surrogate to convert your derived class into a flat proxy surrogate for serialization.

3. Contact your client and get their servicemodel metadata . This will specify the order of fields and will allow c# classes to be automatically generated .

4. Consider switching to XMLSerializer . Documentation here .