[ #55 , Data Validation and Document Types ] (#88) ( not yet implemented

* Add basic example

* Update the example

examples/document-types/README.md

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+# MarkdownDB Schemas Configuration Tutorial
+
+MarkdownDB enables you to establish and enforce the structure of your Markdown content using the Zod library for schema definitions. This tutorial guides you through the process of defining schemas for a blog post, ensuring a mandatory `date` field. The schemas play a crucial role in error prevention and ensure the predicted structure in Markdown files.
+
+## Define Your Schemas
+
+Create a configuration object and use the Zod library to define your schemas. For more information on defining Zod schemas, visit [Zod Documentation - Basic Usage](https://zod.dev/?id=basic-usage).
+In this example, we'll begin by creating a schema for a blog post. For instance:
+```md
+---
+title: blog post
+date: 2023-12-05
+...
+---
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit.
+```
+
+Subsequently, we'll use the `client.indexFolder` method along with the defined schemas to scan and index the folder containing your Markdown files.
+
+```javascript
+// index.js
+import { z } from "zod";
+import { MarkdownDB } from "mddb";
+
+// Define the schemas using Zod
+const schemas = {
+  post: z.object({
+    date: z.string().refine((value) => /\d{4}-\d{2}-\d{2}/.test(value), {
+      message:
+        "Invalid date format. Please use YYYY-MM-DD format for the 'date' field.",
+    }),
+  }),
+};
+
+// Code for initializing the connection
+const client = new MarkdownDB({
+  client: "sqlite3",
+  connection: {
+    filename: "markdown.db",
+  },
+});
+const mddb = await client.init();
+
+// Index the folder with MarkdownDB
+await client.indexFolder({
+  folderPath: contentPath,
+  schemas: schemas,
+});
+```
+
+## How Validation Works
+
+MarkdownDB automatically validates your Markdown content against the defined schemas using Zod. Here's how the validation process works:
+
+- **Schemas Definition:** The `post` schema is defined using Zod's `object` method, specifying the structure of the content.
+- **Validation Errors:** If validation fails, MarkdownDB throws an error with a detailed message. For example:
+  - If the date has an invalid format, it throws an error like this:
+    ```
+    Error: In 'blog.md' for the 'post' schema. Invalid date format. Please use YYYY-MM-DD format for the 'date' field.
+    ```
+  - If a required field is missing, it throws an error like this:
+    ```
+    Error: Missing 'date' field in 'blog.md' for the 'post' schema.
+    ```
+
+Now you have robust schemas in place, ensuring the integrity of your Markdown content. Feel free to extend and customize the schemas to meet the specific requirements of your project.

examples/document-types/index.js

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+import { z } from "zod";
+import { MarkdownDB } from "mddb";
+
+const dbPath = "markdown.db";
+const client = new MarkdownDB({
+  client: "sqlite3",
+  connection: {
+    filename: dbPath,
+  },
+});
+await client.init();
+
+// Define the schemas using zod
+const schemas = {
+  post: z.object({
+    date: z.string().refine((value) => /\d{4}-\d{2}-\d{2}/.test(value), {
+      message:
+        "Invalid date format. Please use YYYY-MM-DD format for the 'date' field.",
+    }),
+  }),
+};
+
+// Index the folder with the files
+await client.indexFolder({
+  folderPath: contentPath,
+  ignorePatterns: ignorePatterns,
+  schemas: schemas
+});
+
+process.exit(0);