# lookup()

```
string lookup(string fidj-file-uri, string key [, string default = ""])
```

The XPath function `lookup` returns the value associated with the `key` in a database file. The database file specified by the `fidj-uri` can be either in JSON or [SHMT](https://github.com/sevenval/SHMT) format. If the `key` is not found, the `default` string will be returned.

* `fidj-file-uri`: FIDJ URI pointing to a local database *file*. The extension

  of the database file must be either lowercase `.json` for a JSON file or lowercase

  `.shmt` for an SHMT file.
* `key`: database key to search for
* `default`: optional value to return if the

  `key` is not found in the database (default is an empty string `""`)

## Using a JSON file

The JSON DB file has to be implemented as a key-value object (SHMT does this automatically):

```javascript
{
  "key1": "value1",
  "key2": [1, 2, 3],
  "key3": {"k":"v"}
  ...
}
```

If a value is either of type `object` or `ordered list of values` (`array`), the value is always converted to a JSON string. By using the [`json-to-xml()`](https://sevenval.gitbook.io/flat/develop/reference/functions/json-to-xml) function, the result string can be translated into a corresponding XML structure.

Example:

```markup
  <xsl:value-of select="lookup('fit://site/databases/db.json', 'key3')" />
```

would result in the string `"{\"k\":\"v\"}"`.

## Debugging

The `lookup` XPath function provides many information or error messages in the `json` [debug channel](https://sevenval.gitbook.io/flat/develop/reference/debugging).

## Examples

```markup
...
  <xsl:value-of select="lookup('fit://project/db/my.json', 'full_name', 'John Doe')" />
...
  <xsl:value-of select="lookup('fit://site/databases/db.shmt', 'key')" />
...
```