doc: formatting IDs (#536)

* doc: formatting IDs

* doc: move default value generator doc to the "modeling" part, add parameter documentation ref guide

* doc: add links to function ref

* remove the unused md file

* update

---------

Co-authored-by: ymc9 <104139426+ymc9@users.noreply.github.com>

Author: sanny-io

docs/modeling/model.md

@@ -144,15 +144,17 @@ model User {
 }
 ```
 
+### Default values
+
 A default value can be specified for a field with the `@default` attribute. The value can be a literal, an enum value, or a supported function call, including:
 
-- `now()`: returns the current timestamp
-- `cuid()`: returns a CUID
-- `uuid()`: returns a UUID
-- `ulid()`: returns a ULID
-- `nanoid()`: returns a Nano ID
-- `autoincrement()`: returns an auto-incrementing integer (only for integer fields)
-- `dbgenerated("...")`: calls a native db function
+- [`now()`](../reference/zmodel/function.md#now): returns the current timestamp
+- [`cuid()`](../reference/zmodel/function.md#cuid): returns a CUID
+- [`uuid()`](../reference/zmodel/function.md#uuid): returns a UUID
+- [`ulid()`](../reference/zmodel/function.md#ulid): returns a ULID
+- [`nanoid()`](../reference/zmodel/function.md#nanoid): returns a Nano ID
+- [`autoincrement()`](../reference/zmodel/function.md#autoincrement): returns an auto-incrementing integer (only for integer fields)
+- [`dbgenerated("...")`](../reference/zmodel/function.md#dbgenerated): calls a native db function
 
 ```zmodel
 model User {
@@ -162,6 +164,15 @@ model User {
 }
 ```
 
+Prefixing and suffixing entity IDs is becoming more common in database design, usually by including the model name in the generated ID. To support this pattern, functions that generate `String` IDs (`cuid()`, `uuid()`, `ulid()`, `nanoid()`) takes an optional `format` argument to allow passing in a pattern that controls the output format. `%s` in the pattern will be replaced by the generated id. For example:
+
+```zmodel
+model User {
+    // generate a UUID v4 with "user_" prefix
+    id String @id @default(uuid(4, "user_%s"))
+}
+```
+
 ## Native type mapping
 
 Besides giving a field a type, you can also specify the native database type to use with the `@db.` series of attributes.

docs/reference/zmodel/function.md

@@ -89,35 +89,54 @@ Functions related to input validation are documented in a [separate page](./inpu
 ### uuid()
 
 ```zmodel
-function uuid(): String {}
+function uuid(version: Int?, format: String?): String {}
 ```
 
 Generates a globally unique identifier based on the UUID spec.
 
+*Parameters:*
+
+- `version` (optional): The UUID version to generate. Supported values are `4` (default) and `7`.
+- `format` (optional): A pattern to control the output format. `%s` in the pattern will be replaced by the generated id. Use escaped `\\%s` to have a literal `%s` in the output.
+
 ### cuid()
 
 ```zmodel
-function cuid(version: Int?): String {}
+function cuid(version: Int?, format: String?): String {}
 ```
 
-Generates a unique identifier based on the [CUID](https://github.com/ericelliott/cuid) spec. Pass `2` as an argument to use [cuid2](https://github.com/paralleldrive/cuid2).
+Generates a unique identifier based on the [CUID](https://github.com/ericelliott/cuid) spec.
+
+*Parameters:*
+
+- `version` (optional): The CUID version to generate. Supported values are `1` (default) and `2`.
+- `format` (optional): A pattern to control the output format. `%s` in the pattern will be replaced by the generated id. Use escaped `\\%s` to have a literal `%s` in the output.
 
 ### nanoid()
 
 ```zmodel
-function nanoid(length: Int?): String {}
+function nanoid(length: Int?, format: String?): String {}
 ```
 
 Generates an identifier based on the [nanoid](https://github.com/ai/nanoid) spec.
 
+*Parameters:*
+
+- `length` (optional): The length of the generated id.
+- `format` (optional): A pattern to control the output format. `%s` in the pattern will be replaced by the generated id. Use escaped `\\%s` to have a literal `%s` in the output.
+
 ### ulid()
 
 ```zmodel
-function ulid(): String {}
+function ulid(format: String?): String {}
 ```
 
 Generates a unique identifier based on the [ULID](https://github.com/ulid/spec) spec.
 
+*Parameters:*
+
+- `format` (optional): A pattern to control the output format. `%s` in the pattern will be replaced by the generated id. Use escaped `\\%s` to have a literal `%s` in the output.
+
 ### now()
 
 ```zmodel