Execute formatted time in a slice with html/template

I'm making this simple webserver that can host my blog, but whatever I do; I can not execute a proper formatted time into my html/template.

Here's what I do:

I've created this struct:

type Blogpost struct {
    Title   string
    Content string
    Date    time.Time
}

Next up I've created this little func that retrieves the blogposts with corresponding title/dates from the Appengine Datastore and return that as a slice:

func GetBlogs(r *http.Request, max int) []Blogpost {
    c := appengine.NewContext(r)
    q := datastore.NewQuery("Blogpost").Order("-Date").Limit(max)
    bp := make([]Blogpost, 0, max)
    q.GetAll(c, &bp)
    return bp
}

Finally, in the blogHandler I create a slice based on the retrieved data from the Appengine Datastore using:

blogs := GetBlogs(r, 10)

Now when I Execute my template called blog like this, the dates of the blogs are being parsed as default dates:

blog.Execute(w, blogs) // gives dates like: 2013-09-03 16:06:48 +0000 UTC

So, me, being the Golang n00b that I am, would say that a function like the following would give me the result I want

blogs[0].Date = blogs[0].Date.Format("02-01-2006 15:04:05") // Would return like 03-09-2013 16:06:48, at least when you print the formatted date that is.

However that results in a type conflict ofcourse, which I tried to solve using:

blogs[0].Date, _ = time.Parse("02-01-2006 15:04:05", blogs[0].Date.Format("02-01-2006 15:04:05")) // returns once again: 2013-09-03 16:06:48 +0000 UTC

It is probably some n00b thing I oversaw once again, but I just can't see how I can't override a time.Time Type in a slice or at least print it in the format that I want.

While I looking for a similar functionality to simply format and render a time.Time type in a html/template, I fortuitously discovered that go's template parser allows methods to be called under certain restrictions when rendering a time.Time type.

For example;

type Post struct {
    Id        int
    Title     string
    CreatedOn time.Time
}

// post is a &Post. in my case, I fetched that from a postgresql
// table which has a datetime column for that field and
// value in db is 2015-04-04 20:51:48

template.Execute(w, post)

and it's possible to use that time in a template like below:

<span>{{ .CreatedOn }}</span>
<!-- Outputs: 2015-04-04 20:51:48 +0000 +0000 -->

<span>{{ .CreatedOn.Format "2006 Jan 02" }}</span>
<!-- Outputs: 2015 Apr 04 -->

<span>{{ .CreatedOn.Format "Jan 02, 2006" }}</span>
<!-- Outputs: Apr 04, 2015 -->

<span>{{.CreatedOn.Format "Jan 02, 2006 15:04:05 UTC" }}</span>
<!-- Outputs: Apr 04, 2015 20:51:48 UTC -->

As a note; my go version is go1.4.2 darwin/amd64

Hope it helps others.

Your Date field has type time.Time. If you format it as a string, and parse it back, you'll once again get a time.Time value, which will still print the default way when the template execution calls its String method, so it's not really solving your problem.

The way to solve it is by providing the template with the formatted time string itself instead of a time value, and you can do that in multiple ways. For example:

• Add a method to your blog post type named FormattedDate or similar, which returns a string properly formatted in the style of your preference. That's the easiest, and probably the nicest way if you don't have a fancy use case.

• Add a string field to your blog type named FormattedDate or similar; that's very similar to the above option, but you have to be careful to set and update the field whenever necessary, so I'd prefer the method option instead.

• If you'd like to format time values in multiple ways within the template, you might also opt to define a template formatter function, so that you might do something like {{post.Date | fdate "02-01-2006 15:04:05"}}. See the documentation on Template.Funcs, the FuncMap type, and this example for details on how to do that.

Update: Sample code for the first option: http://play.golang.org/p/3QYdrDQ1YO

If you output a time.Time in a template it will be converted to a string. This default conversion is what you see. If you need a different format you have two possibilites:

1. Add a `FormatedDate string field to your Blogpost and populate it from Date via Date.Format(whatever)
2. Write and register a formatting filter` in your template (see http://golang.org/pkg/html/template/#Template.Funcs) and use this.