Fluent NHibrnate - Virtual calls in constructor -Best Practice - nhibernate

I have an entity declared similar to this:
public class Comment
{
public Comment(string text, DateTime creationDate, string authorEmail)
{
Text = text;
CreationDate = creationDate;
AuthorEmail = authorEmail;
}
public virtual string Text { get; private set; }
public virtual DateTime CreationDate { get; set; }
public virtual string AuthorEmail { get; private set; }
}
I have taken it from Is it OK to call virtual properties from the constructor of a NHibernate entity?
I get warning as 'Virtual Calls in constructor'.
Though, it doesn't pose any practical issue because virtual members are declared solely for NH to proxy. However, I was wondering if I should move the constructor method to a new factory class with new method being declared as
CreateComment(string text, DateTime creationDate, string authorEmail)
What will be the best practice in this case?
Please note that currently I have 4-5 overloaded constructors in my domain entity. Above is just an example.
Thank you!


I have tested with FluentNHibernate, you can do it like this:
public class Comment
{
private string _text;
private DateTime _creationDate;
private string _authorEmail;
public Comment(string text, DateTime creationDate, string authorEmail)
{
_text = text;
_creationDate = creationDate;
_authorEmail = authorEmail;
}
public virtual string Text
{
get { return _text; }
private set { _text = value; }
}
public virtual DateTime CreationDate
{
get { return _creationDate; }
set { _creationDate = value; }
}
public virtual string AuthorEmail
{
get { return _authorEmail; }
private set { _authorEmail = value; }
}
}


I prefer having a parameterless (default) constructor and constructing like so:
var comment = new Comment {
Text = "Something offensive and political.",
CreationDate = DateTime.Now,
AuthorEmail = "someonestupidwithanopinion17#aol.com"
};
Now the issue doesn't matter.


If your properties are only virtual to accomodate nHibernate, you can just make them encapsulate concrete fields (nhibernate knows how to cope with that: see here (default-access) and here (access).
it's supported in fluent nh as well.

Related

How to map object type field in Nhibernate Auto Mapping

When trying to map, I got this error:
Association references unmapped class: System.Object
My class:
public partial class MessageIdentifier
{
public virtual int ID { get; set; }
public virtual object Item { get; set; }
}
And the convention:
public class MyUsertypeConvention : IPropertyConvention
{
public void Apply(IPropertyInstance instance)
{
if (instance.Type.Name == "Object")
instance.CustomType<string>();
}
}
Kindly suggest how to map?

As a simple (quick, naive) solution - I would suggest to create and map real string property. And then let your setter and getter (or some AOP or listener) to do the "to/from string conversion":
public partial class MessageIdentifier
{
public virtual int ID { get; set; }
public virtual object Item
{
get { return ... my conversion from string; }
set { ItemString = ...my conversion to string; }
}
public virtual string ItemString { get; set; }
}
A smart and preferred (but a bit more challenging) is to create CustomType - which will hide that conversion and support REUSE. Check e.g. here
NHibernate Pitfalls: Custom Types and Detecting Changes
Creating and Testing a Custom NHibernate User Type

Not a satisfactory answer. It doesn't work with class that is generated from xsd by using XML. You can try the following:
public partial class MessageIdentifier
{
public virtual int ID { get; set; }
private object itemField;
public object Item
{
get { return this.itemField; }
set { this.itemField = value; }
}
}

NHibernate Mapping Property Which Depends on Another Property

I have the following class:
public class Widget {
public virtual int Id { get; set; }
[Required]
public virtual WidgetType Type { get; set; }
public virtual string SerializedParameters {
get {
return new XmlSerializer(Parameters.GetType()).Serialize(Parameters);
} set {
Parameters = new XmlSerializer(Assembly
.LoadFrom(Server.MapPath(Type.ModelAssembly))
.GetType(Type.ModelClass)
).Deserialize(value);
}
}
private object _parameters;
public virtual object Parameters {
get {
if (_parameters == null)
_parameters = Activator.CreateInstance(Assembly
.LoadFrom(Server.MapPath(Type.ModelAssembly))
.GetType(Type.ModelClass)
);
return _parameters;
} set { _parameters = value; }
}
}
The Parameters property is not mapped to the database but the SerializedParameters property is. However when it tries to get the information from the database and set the SerializedParameters (which subsequently sets the Parameters) the Type property is null and therefore an exception is thrown. I guess this depends on the order in which NHibernate sets the properties for the Widget but i can't get it to work.
I was wondering if there was a way around this. Appreciate the help. Thanks

moved the deserialization in the getter from the setter because as you said the type is not there yet
public class Widget
{
public virtual int Id { get; set; }
public virtual WidgetType Type { get; set; }
private string _serializedParameters;
private virtual string SerializedParameters {
get
{
return new XmlSerializer(Parameters.GetType()).Serialize(Parameters);
}
set
{
_serializedParameters = value;
}
}
private object _parameters;
public virtual object Parameters
{
get
{
if (_parameters == null)
{
if (!string.IsNullOrEmpty(serializedParameters))
{
// code to deserialize the Parameters and set to Parameters
_parameters = new XmlSerializer(Assembly
.LoadFrom(Server.MapPath(Type.ModelAssembly))
.GetType(Type.ModelClass)
).Deserialize(value);
}
else
{
// no existing parameters, then create new object
_parameters = Activator.CreateInstance(Assembly.LoadFrom(Server.MapPath("~/bin/" + widget.Type.ParametersAssembly + ".dll")).GetType(widget.Type.ParametersClass));
}
}
return _parameters;
}
set { _parameters = value; }
}
}

NHibernate - IUserType For Changing Type?

My application has the following classes:
public class Widget {
public virtual int Id { get; set; }
public virtual WidgetType Type { get; set; }
public virtual string Parameters { get; set; }
}
public class WidgetType {
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual string ParametersAssembly { get; set; }
public virtual string ParametersClass { get; set; }
}
Now if i'd like to update the Parameters for a particular widget i would say something like:
// Get the widget
var widget = GetWidget(1);
// Create an instance of the type parameters class
var parameters = Activator.CreateInstance(Assembly.LoadFrom(Server.MapPath("~/bin/"
+ widget.Type.ParametersAssembly + ".dll")).GetType(widget.Type.ParametersClass));
... Code here to update the parameters
widget.Parameters = new XmlSerializer(parameters.GetType()).Serialize(parameters);
I have to do the reverse when i wish to get the parameters. You can imagine this becomes quite tedious. I was wondering if it was possibly to automatically do this?
I've been looking at the IUserType interface. I found an article which is kind of similar. However my problem is a little more complicated as my type changes based on the type of the widget.
I'd appreciate it if someone could let me know if this is possible and possibly how it could be achieved. Thanks

an easy way
public class Widget
{
public virtual int Id { get; set; }
public virtual WidgetType Type { get; set; }
private string _serializedParameters;
private virtual string SerializedParameters {
get
{
return new XmlSerializer(Parameters.GetType()).Serialize(Parameters);
}
set
{
_serializedParameters = value;
// code to deserialize the Parameters and set to Parameters
var ptype = Assembly.LoadFrom(Server.MapPath("~/bin/" + widget.Type.ParametersAssembly + ".dll")).GetType(widget.Type.ParametersClass);
Parameters = Activator.CreateInstance(ptype);
}
}
private object _parameters;
public virtual object Parameters
{
get
{
if (_parameters == null)
_parameters = Activator.CreateInstance(Assembly.LoadFrom(Server.MapPath("~/bin/" + widget.Type.ParametersAssembly + ".dll")).GetType(widget.Type.ParametersClass));
return _parameters;
}
set { _parameters = value; }
}
}
it can't be in the Parameters property because then you have to get -> alter -> set instead of get -> alter. But you are right that building the parameters object should go in the getter of Parameters because only there we can be sure to have the WidgetType loaded
it is essentially the same as a UserType except that we know that WidgetType is there

JSON.Net - DeserializeObject Format

I'm using JSON.Net to try and deserialize some survey responses from SurveyGizmo.
Here's a snapshot of the data I'm reading in:
{"result_ok":true,
"total_count":"44",
"page":1,
"total_pages":1,
"results_per_page":50,
"data":[
{"id":"1",
"contact_id":"",
"status":"Complete",
"is_test_data":"0",
"datesubmitted":"2011-11-13 22:26:53",
"[question(59)]":"11\/12\/2011",
"[question(60)]":"06:15 pm",
"[question(62)]":"72",
"[question(63)]":"One",
"[question(69), option(10196)]":"10",
I've setup a class as far as datesubmitted but I'm not sure how to setup the class to deserialize the questions given that the amount of questions will change? I also need to capture the option if it's present.
I'm using this code to use the JSON.NET Deserialize function:
Dim responses As Responses = JsonConvert.DeserializeObject(Of Responses)(fcontents)
Classes:
Public Class Responses
Public Property result_OK As Boolean
Public Property total_count As Integer
Public Property page As Integer
Public Property total_pages As Integer
Public Property results_per_page As Integer
Public Overridable Property data As List(Of surveyresponse)
End Class
Public Class SurveyResponse
Public Property id As Integer
Public Property status As String
Public Property datesubmitted As Date
End Class

This trick to support totally crazy mappings is to use JsonConverter and completely replace the parsing for that object, (I apologize for the C#, but I'm no good at VB syntax):
class Program
{
static void Main(string[] args)
{
var result = JsonConvert.DeserializeObject<Responses>(TestData);
}
const string TestData = #"{""result_ok"":true,
""total_count"":""44"",
""page"":1,
""total_pages"":1,
""results_per_page"":50,
""data"":[
{""id"":""1"",
""contact_id"":"""",
""status"":""Complete"",
""is_test_data"":""0"",
""datesubmitted"":""2011-11-13 22:26:53"",
""[question(59)]"":""11\/12\/2011"",
""[question(60)]"":""06:15 pm"",
""[question(62)]"":""72"",
""[question(63)]"":""One"",
""[question(69), option(10196)]"":""10"",
}]}";
}
[JsonObject]
class Responses
{
public bool result_ok { get; set; }
public string total_count { get; set; }
public int page { get; set; }
public int total_pages { get; set; }
public int results_per_page { get; set; }
public SurveyResponse[] Data { get; set; }
}
[JsonObject]
// Here is the magic: When you see this type, use this class to read it.
// If you want, you can also define the JsonConverter by adding it to
// a JsonSerializer, and parsing with that.
[JsonConverter(typeof(DataItemConverter))]
class SurveyResponse
{
public string id { get; set; }
public string contact_id { get; set; }
public string status { get; set; }
public string is_test_data { get; set; }
public DateTime datesubmitted { get; set; }
public Dictionary<int, string> questions { get; set; }
}
class DataItemConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(SurveyResponse);
}
public override bool CanRead
{
get { return true; }
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var value = (SurveyResponse)existingValue;
if (value == null)
{
value = new SurveyResponse();
value.questions = new Dictionary<int, string>()
}
// Skip opening {
reader.Read();
while (reader.TokenType == JsonToken.PropertyName)
{
var name = reader.Value.ToString();
reader.Read();
// Here is where you do your magic
if (name.StartsWith("[question("))
{
int index = int.Parse(name.Substring(10, name.IndexOf(')') - 10));
value.questions[index] = serializer.Deserialize<string>(reader);
}
else
{
var property = typeof(SurveyResponse).GetProperty(name);
property.SetValue(value, serializer.Deserialize(reader, property.PropertyType), null);
}
// Skip the , or } if we are at the end
reader.Read();
}
return value;
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
Now obviously there's a lot more you would want to do to get this really robust, but this gives you the basics of how to do it. There are more lightweight alternatives if you simply need to change property names (either JsonPropertyAttribute or overriding DefaultContractResolver.ResolvePropertyName(), but this gives you full control.

Using IList in Nhibernate, does not get initialized

I basically have:
Public Class Job: MyBaseClass
{
public virtual string JobInformation {get;set;}
...
public virtual List<Item> JobItems {get;set;}
}
I was using a List and initializing it (JobItems = new List();) in the constructor. However, I was getting an Exception (Nhibernate.Collection.Generic.PersistentGenericBag)
I read this question and it said I should use IList instead.
So now I have
public class Job: MyBaseClass
{
public virtual string JobInformation {get;set;}
...
public virtual IList<Item> JobItems {get;set;}
}
public virtual void AddItem(Item item)
{
//snip validation
this.JobItems.Add(item);
}
However, it throws a NullReferenceException because JobItems isn't initialized yet. When does NHibernate initialize this collection? Or how can I solve this issue?

use a backing field and on return make sure it isn't null
public IList<Item> JobItems
{
get { return _jobItems ?? (_jobItems = new List<Item>()); }
set { _jobItems = value; }
}

You should initialize the collection if it hasn't been previously initialized.
private IList<Item> _jobItems;
public IList<Item> JobItems
{
get
{
return _jobItems ?? (_jobItems = new List<Item>());
}
private set
{
_jobItems = value;
}
}