Question

Basically I want to have a single construct to deal with serializing to both JSON and formatted xml. Records worked nicely for serializing to/from json. However XmlSerializer requires a parameterless construtor. I don’t really want to have to go through the exercise of building class objects for these constructs (principle only). I was hoping there could be some shortcut for getting a parameterless constructor onto a record (perhaps with a wioth statement or something). I can’t get it to behave – has anybody in the community had any luck?

module JSONExample
    open System
    open System.IO 
    open System.Net 
    open System.Text 
    open System.Web 
    open System.Xml
    open System.Security.Authentication 
    open System.Runtime.Serialization //add assemnbly reference System.Runtime.Serialization System.Xml
    open System.Xml.Serialization
    open System.Collections.Generic 

    [<DataContract>]            
    type ChemicalElementRecord = { 
        [<XmlAttribute("name")>]
        [<field: DataMember(Name="name") >] 
        Name:string 

        [<XmlAttribute("name")>]
        [<field: DataMember(Name="boiling_point") >] 
        BoilingPoint:string 

        [<XmlAttribute("atomic-mass")>]
        [<field: DataMember(Name="atomic_mass") >] 
        AtomicMass:string 
    } 

    [<XmlRoot("freebase")>]
    [<DataContract>] 
    type FreebaseResultRecord = { 
        [<XmlAttribute("code")>]
        [<field: DataMember(Name="code") >] 
        Code:string 

        [<XmlArrayAttribute("results")>]
        [<XmlArrayItem(typeof<ChemicalElementRecord>, ElementName = "chemical-element")>]
        [<field: DataMember(Name="result") >] 
        Result: ChemicalElementRecord array

        [<XmlElement("message")>] 
        [<field: DataMember(Name="message") >] 
        Message:string 
        } 


    let getJsonFromWeb() = 
        let query = "[{'type':'/chemistry/chemical_element','name':null,'boiling_point':null,'atomic_mass':null}]"
        let query = query.Replace("'","\"") 
        let queryUrl = sprintf "http://api.freebase.com/api/service/mqlread?query=%s" "{\"query\":"+query+"}" 

        let request : HttpWebRequest = downcast WebRequest.Create(queryUrl) 
        request.Method <- "GET" 
        request.ContentType <- "application/x-www-form-urlencoded" 

        let response = request.GetResponse() 

        let result = 
            try 
                use reader = new StreamReader(response.GetResponseStream()) 
                reader.ReadToEnd(); 
            finally 
                response.Close() 

        let data = Encoding.Unicode.GetBytes(result); 
        let stream = new MemoryStream() 
        stream.Write(data, 0, data.Length); 
        stream.Position <- 0L 
        stream



    let test =
        // get some JSON from the web
        let stream = getJsonFromWeb()

        // convert the stream of JSON into an F# Record
        let JsonSerializer = Json.DataContractJsonSerializer(typeof<FreebaseResultRecord>) 
        let result: FreebaseResultRecord = downcast JsonSerializer.ReadObject(stream) 

        // save the Records to disk as JSON 
        use fs = new FileStream(@"C:\temp\freebase.json", FileMode.Create) 
        JsonSerializer.WriteObject(fs,result)
        fs.Close()

        // save the Records to disk as System Controlled XML
        let xmlSerializer = DataContractSerializer(typeof<FreebaseResultRecord>);
        use fs = new FileStream(@"C:\temp\freebase.xml", FileMode.Create) 
        xmlSerializer.WriteObject(fs,result)
        fs.Close()

        use fs = new FileStream(@"C:\temp\freebase-pretty.xml", FileMode.Create) 
        let xmlSerializer = XmlSerializer(typeof<FreebaseResultRecord>)
        xmlSerializer.Serialize(fs,result)
        fs.Close()

ignore(test)

Answer 1

Looks like you can’t change a record to a class – or add a edfault constructor to it.

The example provided (basedof off this article: Link) gets a stream of json from api.freebase.com; we then deserialize into the attributed classes; next serialize it as Json to disk; then serialize it as Xml to disk (using DataContract); finally, with the best controll of the output serialize it as Xml to disk (using XmlSerializer):

Notes:

DataContract(family of) attributes for
DataContractJsonSerializer and
JSON.DataContractJsonSerializer –
these occur over the class names and
the memeber variables. DataContract
stuff was straight forward – and
works on record types as well.

XmlSerializer(family of) attributes
over the class and the Property
Getter/Setter. This requires the type
is an object with a default
constructor, and property Getters and
Setters w/ attributes associated with
each of them. If a Property doesn’t
have eitehr a getter or a setter it
will not serialize – which was a
suprise (I imagined the default
onstructor would ensure that the
object had defulat values upon
deserialization and the setters would
update with whatever was serialized –
but no this isn’t the case).

Another nifty (sigh) thing about
XmlSerialization is that the classes
can’t be contained within a module. So
we move the types up to a namespace…

namespace JSONExample
    open System
    open System.IO 
    open System.Net 
    open System.Text 
    open System.Web 
    open System.Xml
    open System.Security.Authentication 
    open System.Runtime.Serialization //add assemnbly reference System.Runtime.Serialization System.Xml
    open System.Xml.Serialization
    open System.Collections.Generic 

    [<DataContract>]            
    type ChemicalElementRecord() =  
        [<field: DataMember(Name="name") >] 
        let mutable name: string  = ""
        
        [<field: DataMember(Name="boiling_point") >] 
        let mutable boilingPoint: string =""

        [<field: DataMember(Name="atomic_mass") >] 
        let mutable atomicMass: string  = ""

        [<XmlAttribute("name")>]
        member this.Name with get() = name and set v = name <- v
        
        [<XmlAttribute("boiling-point")>]
        member this.BoilingPoint with get()  = boilingPoint  and set v = boilingPoint <- v

        [<XmlAttribute("atomic-mass")>]
        member this.AtomicMass with get() = atomicMass  and set v = atomicMass <- v
    
    [<XmlRoot("freebase")>]
    [<DataContract>] 
    type FreebaseResultRecord() =  
        
        [<field: DataMember(Name="code") >] 
        let mutable code: string = ""

        [<field: DataMember(Name="result") >] 
        let mutable result: ChemicalElementRecord array = Array.empty
        
        [<field: DataMember(Name="message") >] 
        let mutable message: string = ""

        [<XmlElement("message")>] 
        member this.Message with get() : string = message and set v = message <- v

        [<XmlArrayAttribute("chemical-elements")>]
        [<XmlArrayItem(typeof<ChemicalElementRecord>, ElementName = "chemical-element")>]
        member this.Result with get() = result and set v = result <- v
        
        [<XmlAttribute("code")>]
        member this.Code with get() = code and set v = code <- v
 
    module Test = 
        let getJsonFromWeb() = 
            let query = "[{'type':'/chemistry/chemical_element','name':null,'boiling_point':null,'atomic_mass':null}]"
            let query = query.Replace("'","\"") 
            let queryUrl = sprintf "http://api.freebase.com/api/service/mqlread?query=%s" "{\"query\":"+query+"}" 
          
            let request : HttpWebRequest = downcast WebRequest.Create(queryUrl) 
            request.Method <- "GET" 
            request.ContentType <- "application/x-www-form-urlencoded" 
          
            let response = request.GetResponse() 
          
            let result = 
                try 
                    use reader = new StreamReader(response.GetResponseStream()) 
                    reader.ReadToEnd(); 
                finally 
                    response.Close() 
          
            let data = Encoding.Unicode.GetBytes(result); 
            let stream = new MemoryStream() 
            stream.Write(data, 0, data.Length); 
            stream.Position <- 0L 
            stream


          
        let test =
            // get some JSON from the web
            let stream = getJsonFromWeb()
            
            // convert the stream of JSON into an F# Record
            let JsonSerializer = Json.DataContractJsonSerializer(typeof<FreebaseResultRecord>) 
            let result: FreebaseResultRecord = downcast JsonSerializer.ReadObject(stream) 

            // save the Records to disk as JSON 
            use fs = new FileStream(@"C:\temp\freebase.json", FileMode.Create) 
            JsonSerializer.WriteObject(fs,result)
            fs.Close()

            // save the Records to disk as System Controlled XML
            let xmlSerializer = DataContractSerializer(typeof<FreebaseResultRecord>);
            use fs = new FileStream(@"C:\temp\freebase.xml", FileMode.Create) 
            xmlSerializer.WriteObject(fs,result)
            fs.Close()

            use fs = new FileStream(@"C:\temp\freebase-pretty.xml", FileMode.Create) 
            let xmlSerializer = XmlSerializer(typeof<FreebaseResultRecord>)
            xmlSerializer.Serialize(fs,result)
            fs.Close()
            

        ignore(test)