From 614d1c5f023ccc8d0278b81e69b19401d51fb199 Mon Sep 17 00:00:00 2001
From: Tapac <fantocci@gmail.com>
Date: Wed, 19 Jun 2019 00:27:22 +0300
Subject: [PATCH] Custom functions description

---
 Functions.md | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/Functions.md b/Functions.md
index c0ef220..dd0f53c 100644
--- a/Functions.md
+++ b/Functions.md
@@ -1,3 +1,7 @@
+* [How to use functions](#how-to-use-functions)
+* [String functions](#string-functions)
+* [Aggregating functions](#aggregating-functions)
+* [Custom functions](#custom-functions)
 
 ## How to use functions
 In cases when you want to retrieve function result from a query you have to declare function as a variable like:
@@ -35,4 +39,32 @@ val (min, max, avg) = FooTable.slice(minId, maxId, averageId).selecAll().map {
     Triple(it[minId], it[maxId], it[averageId]) 
 }
 
-```
\ No newline at end of file
+```
+
+## Custom functions
+If you can't find your most loved function used in your database (as Exposed provides only basic support for classic SQL functions) you can define your own functions.
+
+Since Exposed 0.15.1 there multiple options to define custom functions:
+1. Function without parameters:
+```kotlin
+val sqrt = FooTable.id.function("SQRT")
+```
+In SQL representation it will be `SQRT(FooTable.id)`
+
+2. Function with additional parameters:
+```kotlin
+val replacedName = CustomFunction<String?>("REPLACE", VarCharColumnType(), FooTable.name, stringParam("foo"), stringParam("bar"))
+
+``` 
+`CustomFunction` class accept function name as a first parameter and resulting column type as second, after that you can provide any amount of parameters with will be separated by a comma.
+
+There are also shortcuts for string, long and datetime functions:
+* `CustomStringFunction`
+* `CustomLongFunction`
+* `CustomDateTimeFunction`
+
+The code above could be simplified to:
+```kotlin
+val replacedName = CustomStringFunction("REPLACE", FooTable.name, stringParam("foo"), stringParam("bar"))
+
+```