---
title: Query
sidebar_label: Query
---

Queries are exposed by the platform in the form of `:queries` key in the capacities map.
Only those queries which are exposed can be either referenced by hook property (when the property is of the type `:query`),
or used to read data in let block in view (eq `(let [network-name (query [:get-in [:network :name]])] [text {} network-name])`).

## Query as hook property

To refer to some query via hook property (might be required for some host app hooks), the property must be defined as `:query` type
by the app-hook and extension must correctly refer to query from capacities map.

### Example

```clojure
;; App hook code in host application
(reify host/AppHook
  (id [_] :wallet-asset)
  (properties [_] {:able-to-send :query}))
  
;; Capacities map in the host application
{:capacities {:queries #{:network-up}}}

;; Extension hook data
hooks/wallet-asset.next-coin
{:able-to-send :network-up}
```

## Queries in views

To use some queries in extension defined view, the query must be exposed via capacities map of the host platform.

## Example

```clojure
;; Capacities map in the host application
{:capacities {:queries #{:get-in}}}

;; Extension view data
views/coin-item
[view {}
  (let [current-network (query [:get-in [:networks :current :name]])]
    [text {} "Current network: "]
      [text {} current-network]])
```

## Queries permission checking

There is a special treatment for generic query `:get-in` where it's data path (where to read data from app-state exposed by host platform)
is checked against the declared `[:permissions :read]` map in the capacities. 
Whenever this check fails (extension is reading data in view not exposed the host), meaningfull parse error will be produced.