How to use Fluent style syntactic sugar with c# property declaration

Question

I never used the fluent code style before. So this is hte first time I tried to develop something in the fluent style with a C# property declaration, but I get an error. Can anyone help me?

public class MailTemplate
{
    string _MailBody = "";
    public MailTemplate MailBody
    {
        get { return _MailBody; }
        set { _MailBody = value ; }
    }

    string _Subject = "";
    public MailTemplate Subject
    {
        get { return _Subject; }
        set { _Subject = value; }
    }

    string _MailFrom = "";
    public MailTemplate MailFrom
    {
        get { return _MailFrom; }
        set { _MailFrom = value; }
    }
}

Please help me how I could assign or initialize the mail body and later also can read with same property name. I think a property cannot be used in case of fluent style development. Need some light here.

Daniel Hilgarth · Accepted Answer · 2021-03-24T08:51:55.063

A fluent builder interface for the MailTemplate class would look something like this:

public class MailTemplateBuilder
{
    string _body;
    string _subject;
    string _sender;

    public MailTemplateBuilder WithBody(string body)
    {
        _body = body;
        return this;
    }

    public MailTemplateBuilder WithSubject(string subject)
    {
        _subject = subject;
        return this;
    }

    public MailTemplateBuilder WithSender(string sender)
    {
        _sender = sender;
        return this;
    }

    public MailTemplate Build()
    {
        return new MailTemplate(_sender, _subject, _body);
    }
}

Usage would look like this:

var template = _builder.WithBody("body")
                       .WithSubject("subject")
                       .WithSender("sender")
                       .Build();

Another approach would be to use extension methods:

public static class MailTemplateBuilder
{
    public static MailTemplate WithBody(this MailTemplate item, string body)
    {
        item.MailBody = body;
        return item;
    }

    public static MailTemplate WithSubject(this MailTemplate item, string subject)
    {
        item.MailSubject = subject;
        return item;
    }

    public static MailTemplate WithSender(this MailTemplate item, string sender)
    {
        item.MailFrom = sender;
        return item;
    }
}

Usage would now look like this:

var template = new MailTemplate().WithBody("body")
                                 .WithSubject("subject")
                                 .WithSender("sender");

Please note:
In both cases, the MailTemplate class is not polluted with code for this fluent interface. It would be a simple class:

public class MailTemplate
{
    public string MailBody { get; set; } = "";
    public string Subject { get; set; } = "";
    public string MailFrom { get; set; } = "";
}

So, after you created that instance with any one of the provided fluent interfaces, you can simply read the values by accessing the properties:

var body = template.MailBody;

What's the need of build() method in this case? It works just like an old clone method — usr-local-ΕΨΗΕΛΩΝ, Dec 07 '12 at 11:06
@djechelon: No. Look again, there are two classes here. A builder and the actual template. I don't like poluting the model with code for a fluent interface. — Daniel Hilgarth, Dec 07 '12 at 11:09
i just need to know how could i read back the data. suppose WithBody("body") i can set data with WithBody("body") but how could i read back. — Thomas, Dec 07 '12 at 11:25
@Thomas: Please see update of my answer. I added the code of your `MailTemplate` class and showed how to read the values. — Daniel Hilgarth, Dec 07 '12 at 11:41

score 4 · Answer 2 · answered Dec 07 '12 at 11:01

4

Some frameworks e.g. FluentNHibernate just pass themselves as a lambda for this:

MailTemplate
    .ConfigureWith(mt => mt.MailBody = "hello world")
    .ConfigureWith(mt => mt.MailFrom = "rdingwall@gmail.com")
    .DoSomeOtherStuff()
    .Build();

The implementation for this would be:

public class MailTemplate
{
    // regular auto properties
    public string MailFrom { get; set; }
    public string MailBody { get; set; }

    public MailTemplate ConfigureWith(Action<MailTemplate> func)
    {
        func(this);
        return this;
    }

    ...
}

answered Dec 07 '12 at 11:01

Richard Dingwall

2,692
1
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your ConfigureWith() function expects one delegate but when u use the code like .ConfigureWith(mt => mt.MailBody = "hello world") it means you are passing string data to ConfigureWith() function but it expects one delegate. it is bit confusing for me. can u tell how it works. thanks – Thomas Dec 07 '12 at 12:21
another important thing is can i use your code in .net version 2.0 ?? – Thomas Dec 07 '12 at 12:41
when i am trying to compile your code in c# v2.0 then i am getting error. c# 2.0 does not support lambda? – Thomas Dec 07 '12 at 13:21
It's called a lambda expression, it's a shorthand form of a delegate that's easier to read. In this case, assigning a string value to a property. And yes I just checked, it compiles fine in VS2010 targeting .NET 2.0. – Richard Dingwall Dec 07 '12 at 17:37
ConfigureWith not static. `new MailTemplate().ConfigureWith` ? – Kiquenet Mar 23 '21 at 08:47

score 2 · Answer 3 · answered Dec 07 '12 at 11:03

You can't use properties like that to write a fluent interface - the fields are of type string but your properties all try to return a MailTemplate.

Instead of properties, make these into methods that can be chained together.

public class MailTemplate
{
    string _MailBody = "";

    public MailTemplate Body(string mailBody)
    {
        _MailBody = mailBody;
        return this;
    }

    ...

score 2 · Answer 4 · answered Jan 28 '21 at 11:37

As @Richard said, FluentNHibernate just pass themselves as a lambda. you can also do the same using c#.

public class MailTemplate
{
   
    public string To { get; set; }
    public string From { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }
    public string Attachement { get; set; }

    public static MailTemplate Configure { get => new MailTemplate(); }


    public MailTemplate With(Action<MailTemplate> func)
    {
        func(this);
        return this;
    }

    internal void Build()
    {
        Console.WriteLine("Sending the mail....");
    }
}

This is how to call this method

MailTemplate
            .Configure
                .With(mt => mt.To = "michaelameyaw7@gmail.com")
                .With(mt => mt.From = "persol.system@gmail.com")
                .With(mt => mt.Subject = "Fluent Try Test")
                .With(mt => mt.Body = "Hello, this is mail body")
                .With(mt => mt.Attachement = "file.pdf")
           .Build();

How to use Fluent style syntactic sugar with c# property declaration

4 Answers4

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