Using a template to display data, we can make use of some template functions to improve the presentation. So far we've used {{ . }} to insert textual representations of the parameters, and so had to wrap them in <pre> tags to ensure they displayed properly. Now we can use the template-based render function to render data as an HTML table:

import("http")

route := {method:str    path:str,   relgen:str}{ 
         ["",           "/",        "index_handler"]
}

index_handler := {
    method:str, path:str, 
    response:tuple{header:{k:str, seq:int, v:str}, status:int, body:str},
} begin
    response := http.response{*, 
        body:=execute_template("b1", "hello1", tuple{mydata:=S})
    }
    yield
end


main := {} begin
    template_register(batch_name:="b1", template:=dee(
        template_name:="hello1", 
        template_content:=
        "<!doctype html><h1>Data Server</h1> {{ render .mydata }}"
    ))

    res := http.serve(route:=route)
    print(res)
end

Notice the added render inside the template bracket-pairs. In a browser, hitting http://localhost:8080 would now give:

Data Server

SNO	SNAME	STATUS	CITY
S1	Smith	20	London
S2	Jones	10	Paris
S3	Blake	30	Paris
S4	Clark	20	London
S5	Adams	30	Athens

This HTML table is a great improvement, since it will display correctly on a variety of devices and can be styled using CSS, etc.

However, we're still rendering a relvar, which has no left-to-right nor top-to-bottom order, so the render order is arbitrary and could change each time the page is rendered.

To fix that, we should instead render Ra tables. A Ra table is an array of tuples, and as such does have a top-to-bottom ordering and, when rendered, each tuple has a specific left-to-right ordering.

order

One way to get a Ra table is to use the Ra order function, which takes a relation expression and a list of attributes to order by. It isn't a relational operation, however: the output table is no longer a relation and so relational operations such as project and filter are no longer applicable. It should be considered a final presentation function to convert from relation-land to fixed-display-land (a bit like presenting a date in a string format suited to a given locale).

order(S, {SNO})

SNO SNAME STATUS CITY

S1 Smith 20 London
S2 Jones 10 Paris
S3 Blake 30 Paris
S4 Clark 20 London
S5 Adams 30 Athens

A reverse ordering can be done by prefixing an attribute with -, e.g.

order(S, {-CITY, -SNO})

SNO SNAME STATUS CITY

S3 Blake 30 Paris
S2 Jones 10 Paris
S4 Clark 20 London
S1 Smith 20 London
S5 Adams 30 Athens

SNO	SNAME	STATUS	CITY
S3	Blake	30	Paris
S2	Jones	10	Paris
S4	Clark	20	London
S1	Smith	20	London
S5	Adams	30	Athens

And an extra parameter can be given to limit the number of rows (after ordering), e.g.

order(S, {SNO}, 3)

SNO SNAME STATUS CITY

S1 Smith 20 London
S2 Jones 10 Paris
S3 Blake 30 Paris

Again, these are HTML tables, and now we control the top-to-bottom ordering. The left-to-right ordering is also now fixed, at least, but notice that we didn't say what it was. To do that, we'll need to either:

Use the Ra paginate function to specify not only the top-to-bottom order but also a left-to-right attribute order

Iterate over each tuple's attributes in a given order in the template

Next we'll see how the paginate function can help.

Tables

Data Server

order