Renderers

Renderers attach display metadata to aliased SELECT columns. They are parsed and validated by flyql but never affect SQL or matcher output. Unlike transformers, which change what the database returns, renderers describe how your application should render a value — interpretation is entirely your responsibility.

Post-alias pipe syntax

A renderer chain comes after the alias, separated by a pipe (|):

url as link|href("http://{{value}}")

The alias is required. A column without an alias cannot carry renderers.

Chained renderers

Stack multiple renderers with additional pipes:

url as link|href("http://{{value}}")|badge("info")

Renderers are parsed left-to-right into an ordered list. Chain semantics are entirely up to your application — flyql does not impose an input/output type system on renderers.

Renderers and transformers together

Transformers run before the alias; renderers run after:

url|upper as u|href("https://{{value}}")

The transformer upper affects the generated SQL. The renderer href does not.

No-argument renderers

Renderers without arguments parse the same as argument-less transformers:

url as link|plain

Enabling renderers

Renderer parsing is opt-in via a parser capability flag:

Python

from flyql.columns import parse
cols = parse('url as link|href("/{{value}}")',
             capabilities={"transformers": True, "renderers": True})

Go

import "github.com/iamtelescope/flyql/golang/columns"
caps := columns.Capabilities{Transformers: true, Renderers: true}
cols, _ := columns.Parse(`url as link|href("/{{value}}")`, caps)

JavaScript

import { parse } from 'flyql/columns'
const cols = parse('url as link|href("/{{value}}")',
    { transformers: true, renderers: true })

When renderers is false (the default), post-alias | raises a ParserError with errno 11 and the message "renderers are not enabled".

Empty default registry

Unlike TransformerRegistry.default_registry(), which ships four built-in transformers (upper, lower, len, split), RendererRegistry.default_registry() is empty by design. flyql core makes no assumptions about your rendering technology (HTML, markdown, React, Vue, etc.). You must register your own renderers before the validator will recognize them.

This means that for renderers to be useful in a validator or editor, you must provide a registry; otherwise every referenced renderer will produce an unknown_renderer diagnostic.

Renderers vs. transformers

Concern	Transformers	Renderers
Position in syntax	before alias	after alias
Affects generated SQL	yes	no
Affects matcher output	yes	no
Default registry	4 built-ins	empty
Input/output type system	yes (chain typing)	no
Interpretation	flyql executes	your app executes

See Custom Renderers for registration and validation hooks.