Generating realistic example values

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## Library Version(s)
1.1.11

## Problem

I'm experimenting with compojure-api for documenting a new set of APIs with Prismatic Schema. It;s working well so far, though I have one issue which is not obvious how to resolve - how to generate realistic example values for an input / output schema.

Currently I get Example Values in the swagger UI like this:

```
{
"name": "string",
"description": "string",
"type": "assetClass1",
"ownerID": "string"
"dateCreated": "2018-11-19T01:25:04.282Z",
}
```

In this case, I need ownerID to be a 64 character hex string which satisfies a custom `valid-user-id?` predicate, which defined in Schema as something like:

```
(s/defschema UserID
(s/constrained s/Str valid-user-id? "Valid User ID"))
```

However it's not clear how to get compojure-api to generate valid values which satisfy the constraint (The value "string" doesn't....) and display these to the user in the Swagger UI.

Is there a way to do this? Ideally I would like to be able to specify a custom generator for the schema, which I build easily enough with `test.check` but how do I get that to be reflected in the Swagger UI?

Any help much appreciated!

Start by tracing how Prismatic Schema definitions become Swagger UI example values, then compare that path with the custom generator described using test.check. The issue is complete when a schema can provide realistic values satisfying constraints, and those values appear in the generated Swagger UI examples.

Written by the indexing model from the issue text.