Extend Func using Django's template engine #117

import pgtrigger
from django.template import Context, Template


class TemplateFunc(pgtrigger.Func):
    def render(self, model):
        fields = {field.name: field for field in model._meta.fields}
        columns = {field.name: field.column for field in model._meta.fields}
        template = Template(self.func)
        context = Context({"meta": model._meta, "fields": fields, "columns": columns})
        return template.render(context)

   class Meta:
        triggers = [
            pgtrigger.Trigger(
                name="product_upsert",
                operation=pgtrigger.Insert,
                timing=pgtrigger.Immediate,
                when=pgtrigger.After,
                func=TemplateFunc(
                    """
                        IF EXISTS (
                            SELECT *
                            FROM {{ meta.db_table }}
                            WHERE {{ columns.gtin }}=NEW.{{ columns.gtin }} OR (
                                {{ columns.category }}=NEW.{{ columns.category }} AND
                                {{ columns.subcategory }}=NEW.{{ columns.subcategory }} AND
                                {{ columns.vendor }}=NEW.{{ columns.vendor }} AND
                                {{ columns.model }}=NEW.{{ columns.model }}
                            )
                        ) THEN
                            UPDATE {{ meta.db_table }} SET
                            {% for column in columns %}
                            {% if column != "id" and column != "created" %}
                                {{ column }}=NEW.{{ column }}{% if not forloop.last %},{% endif %}
                            {% endif %}
                            {% endfor %}
                            WHERE {{ columns.gtin }}=NEW.{{ columns.gtin }} OR (
                                {{ columns.category }}=NEW.{{ columns.category }} AND
                                {{ columns.subcategory }}=NEW.{{ columns.subcategory }} AND
                                {{ columns.vendor }}=NEW.{{ columns.vendor }} AND
                                {{ columns.model }}=NEW.{{ columns.model }}
                            );
                            RETURN NULL;
                        ELSE
                            RETURN NEW;
                        END IF;
                    """
                ),
            ),
        ]