Filter

Basic Syntax

Filter in Novi has a familiar syntax. For example, to filter objects with tags corgi and funny, you can use the following filter:

corgi funny

A corgi that is not funny:

corgi -funny

dogs or cats:

dog/cat

You can filter by tags' values, too. Values can be quoted with double quotes.

@=image corgi
@!=video meme
@title="My corgi"

Use % to filter tag values that contain a specific string.

@title % corgi

Use parentheses to group tags.

vlog (dog/cat) -(meme/funny)

Use brackets [] to add common prefix to tags. For instance, the following filter

@[title="My corgi" res="1920x1080"] corgi

is expanded to

@title="My corgi" @res="1920x1080" corgi

Event Filters

We can subscribe to object events using filters. The logic is simple: when a object is created / updated / deleted, Novi checks if the object matches the filter. If it does, the subscriber is notified.

However, when it comes down to actual implementation, we may find it counter-intuitive. For example, I want to listen to all objects' title changes. I write the following filter:

@title

But that'll notify me every time when a object containing @title property is created / updated / deleted. Luckily, we have three new operators to help us out:

• ~tag: Listen to the tag's creation / modification / deletion.
• !tag: Listen to the tag's deletion.
• +tag: Listen to the tag's creation / modification.

These operators can be combined with other operators:

~@title/~@res corgi -(~meme)

Event filtering operators are only useful when used with subscribe. They are not supposed to be used in normal object queries.