Adding 'has' func to determine if an object has a named key

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/README.md b/README.md
index 6969686b..a9c6a41d 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,8 @@ Gomplate is an alternative that will let you process templates which also includ
 				- [Example](#example)
 			- [`trim`](#trim)
 				- [Example](#example)
+			- [`has`](#has)
+				- [Example](#example)
 			- [`json`](#json)
 				- [Example](#example)
 			- [`jsonArray`](#jsonarray)
@@ -389,6 +391,39 @@ $ FOO="  world " | gomplate < input.tmpl
 Hello, world!
 ```
 
+#### `has`
+
+Has reports whether or not a given object has a property with the given key. Can be used with `if` to prevent the template from trying to access a non-existent property in an object.
+
+##### Example
+
+_Let's say we're using a Vault datasource..._
+
+_`input.tmpl`:_
+```go
+{{ $secret := datasource "vault" "mysecret" -}}
+The secret is '
+{{- if (has $secret "value") }}
+{{- $secret.value }}
+{{- else }}
+{{- $secret | toYAML }}
+{{- end }}'
+```
+
+If the `secret/foo/mysecret` secret in Vault has a property named `value` set to `supersecret`:
+
+```console
+$ gomplate -d vault:///secret/foo < input.tmpl
+The secret is 'supersecret'
+```
+
+On the other hand, if there is no `value` property:
+
+```console
+$ gomplate -d vault:///secret/foo < input.tmpl
+The secret is 'foo: bar'
+```
+
 #### `json`
 
 Converts a JSON string into an object. Only works for JSON Objects (not Arrays or other valid JSON types). This can be used to access properties of JSON objects.