Is it possible to call a struct method inside a Tera html template?

help
1

Hi,

Currently, I'm learning how to render HTML templates via Tera. Here is my test case if you wish to setup the very same project in your local environment by creating a new binary crate and verify it

Cargo.toml

[package]
name = "project_01"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
tera = "1"
serde = { version = "1.0.137", features = ["derive"] }

At the same directory level as Cargo.toml I have created a directory named templates with the following two files:

index.html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Test tera</title>
    <meta name="Tera_tutorial" content="Tera tutorial">
    <meta name="author" content="Practice">
    <link rel="stylesheet" type="text/css" href="styles.css">
    <script src=""></script>
  </head>
  <body>
    {% if users  %}

    <div class="div_table">
          <!-- Table header -->
          <div class="div_table_row">
            <div class="div_table_cell div_table_header">
              <p>First name</p>
            </div>
            <div class="div_table_cell div_table_header">
              <p>Last name</p>
            </div>
            <div class="div_table_cell div_table_header">
              <p>Email</p>
            </div>
          </div>

          <!-- Users table content -->
          {% for user in users %}
          <div class="div_table_row">
            <div class="div_table_cell">
              <p>{{ user.first_name }}</p>
            </div>
            <div class="div_table_cell">
              <p>{{ user.last_name }}</p>
            </div>
            <div class="div_table_cell">
              <p>{{ user.get_email() }}</p>
            </div>
          </div>
          {% endfor %}
    </div>
    {% endif %}
 
  </body>
</html>

And its CSS file in the same directory: styles.css

@import url('https://fonts.googleapis.com/css?family=Open+Sans');

.div_table {
    display: table;
    border-collapse: collapse;
}

.div_table_row {
    display: table-row;
}

.div_table_header {
    font-weight: bold;
    text-align: center;
}

.div_table_cell {
    display: table-cell;
    padding-left: 10px;
    padding-right: 10px;
    font-family: "Open Sans";
    font-size: 11px;
    border-top: 1px solid #000000;
}

And finally the main program : main.rs


use std::fs;
use tera::Tera;
use tera::Context;
use serde::Serialize;


#[derive(Debug, Serialize)]
struct User {
    first_name: String,
    last_name: String,
}

impl User {
    fn get_email(&self) -> String {
        format!(
            "{}{}{}{}",
            self.first_name,
            ".",
            self.last_name,
            "@mycorporate.com"
        )
    }
}

fn init() -> Result<String, tera::Error> {
    // Use globbing
    let tera = match Tera::new("templates/*.html") {
        Ok(t) => t,
        Err(e) => {
            println!("Parsing error(s): {}", e);
            ::std::process::exit(1);
        }
    };

    let mut users: Vec<User> = Vec::new();

    users.push(User {
        first_name: String::from("fname-01"),
        last_name: String::from("lname-01"),
    });

    users.push(User {
        first_name: String::from("fname-02"),
        last_name: String::from("lname-02"),
    });

    users.push(User {
        first_name: String::from("fname-03"),
        last_name: String::from("lname-03"),
    });

    let mut context = Context::new();
    context.insert("users", &users);

    let result = {
        tera.render("index.html", &context)?
    };

    Ok(result)
}

fn main() -> std::io::Result<()> {
    let result = init();
    match result {
        Ok(value) => {
            let output_file_name = "templates/result_template.html";
            fs::File::create(output_file_name).unwrap();
            fs::write(output_file_name, value).unwrap();
            ()
        },
        Err(e) => {
            panic!("{}", e);
        }
    }

    Ok(())
}

This fails with the following error message:

* Failed to parse "templates\\index.html"
  --> 39:35
   |
39 |               <p>{{ user.get_email() }}</p>␍␊
   |                                   ^---
   |
   = expected `or`, `and`, `not`, `<=`, `>=`, `<`, `>`, `==`, `!=`, `+`, `-`, `*`, `/`, `%`, a filter, or a variable end (`}}`)
error: process didn't exit successfully: `target\debug\project_01.exe` (exit code: 1)

cargo-run exited abnormally with code 1 at Thu May 26 16:55:06

And this is the part of my HTML template that causes the error:

          <div class="div_table_cell">
              <p>{{ user.get_email() }}</p>
          </div>

Therefore, I would like to know whether is possible to call a struct's method in Tera templates. I mean, in the above code, I can use {{ user.first_name }} and {{ user.last_name }} which are both defined in User struct. So I don't understand why the method syntax on the same struct which returns an expression (String) causes a problem. Is it that in Tera it is impossible to call methods or it's me who's not writing and calling the function correctly in the template?

Thanks in advance

2

When you insert into a Context, the data gets serialized into a Value. So the method doesn't exist from the template's point of view, as it's no longer operating on a User.

I would recommend either:

  • Inserting the email into the context seperately.
  • Converting the User into a form that includes the email (either by manually converting to Value, or by defining another struct and converting to that), and then put that into the context instead.
2 Likes
3

Thank you very much for your answer.

Indeed, now that I'm looking to the source code of the Context, this is what we can see:

pub struct Context {
    data: BTreeMap<String, Value>,
}

Indeed, it's all about static values and there is no way to call functions/methods at run time while rendering. This is very constraining as I'll have really loads of such calls in my project. But I think even in Java and other languages/environments similar limits should exist.

The example, that I provided was just a simple example to see whether it was possible to call a method/function "during" the rendering and in this particular example of course I could have provided the email field in the same User structure.

Thank you very much for your time and clarifying this.

[Edit] :

And here is finally how I changed the code by picking the first solution that you suggested, that is, inserting emails separately to the context:

main.rs


use std::fs;
use tera::Tera;
use tera::Context;
use serde::Serialize;


#[derive(Debug, Serialize)]
struct User {
    userid: String,
    first_name: String,
    last_name: String,
}

impl User {
    fn get_email(&self) -> String {
        format!(
            "{}{}{}{}",
            self.first_name,
            ".",
            self.last_name,
            "@mycorporate.com"
        )
    }
}

fn init() -> Result<String, tera::Error> {
    // Use globbing
    let tera = match Tera::new("templates/*.html") {
        Ok(t) => t,
        Err(e) => {
            println!("Parsing error(s): {}", e);
            ::std::process::exit(1);
        }
    };

    let mut users: Vec<User> = Vec::new();

    users.push(User {
        userid: String::from("id-01"),
        first_name: String::from("fname-01"),
        last_name: String::from("lname-01"),
    });

    users.push(User {
        userid: String::from("id-02"),
        first_name: String::from("fname-02"),
        last_name: String::from("lname-02"),
    });

    users.push(User {
        userid: String::from("id-03"),
        first_name: String::from("fname-03"),
        last_name: String::from("lname-03"),
    });

    let mut context = Context::new();
    context.insert("users", &users);

    let mut emails: Vec<(String, String)> = Vec::new();
    for user in users {
        emails.push((user.userid.clone(), user.get_email().clone()));
    }
    context.insert("emails", &emails);

    let result = {
        tera.render("index.html", &context)?
    };

    Ok(result)
}

fn main() -> std::io::Result<()> {
    let result = init();
    match result {
        Ok(value) => {
            let output_file_name = "templates/result_template.html";
            fs::File::create(output_file_name).unwrap();
            fs::write(output_file_name, value).unwrap();
            ()
        },
        Err(e) => {
            panic!("{}", e);
        }
    }

    Ok(())
}

And the new version of my template : index.html


<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Test tera</title>
    <meta name="Tera_tutorial" content="Tera tutorial">
    <meta name="author" content="Practice">
    <link rel="stylesheet" type="text/css" href="styles.css">
    <script src=""></script>
  </head>
  <body>
    {% if users  %}

    <div class="div_table">
          <!-- Table header -->
          <div class="div_table_row">
            <div class="div_table_cell div_table_header">
              <p>First name</p>
            </div>
            <div class="div_table_cell div_table_header">
              <p>Last name</p>
            </div>
            <div class="div_table_cell div_table_header">
              <p>Email</p>
            </div>
          </div>

          <!-- Users table content -->
          {% for user in users %}
          <div class="div_table_row">
            <div class="div_table_cell">
              <p>{{ user.first_name }}</p>
            </div>
            <div class="div_table_cell">
              <p>{{ user.last_name }}</p>
            </div>
            <div class="div_table_cell">
              {% for email in emails %}
                {% if email.0 == user.userid %}
                  <p>{{ email.1 }}</p>
                {% endif %}
              {% endfor %}
            </div>
          </div>
          {% endfor %}
    </div>
    {% endif %}
 
  </body>
</html>

Thanks again for your help.

1 Like
4

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