docs: add repository inserting data page (#26)

Author: kiaking

docs/guide/repository/inserting-data.md

@@ -1,3 +1,162 @@
 # Repository: Inserting Data
 
-Coming soon...
+You may insert new data or update existing data through various repository methods. All data created through Vuex ORM gets persisted in Vuex Store.
+
+In this section, it assumes you're familiar with the usage of repository. If not, please read through the [Repository: Getting Started](./getting-started) page first.
+
+## Inserting Data
+
+The repository provides an `insert` method for inserting records into the store. The `insert` method accepts an object of field and value pairs.
+
+```js
+store.$repo(User).insert({ id: 1, name: 'John Doe' })
+```
+
+You may also pass an array of objects to update multiple records at once.
+
+```js
+store.$repo(User).insert([
+  { id: 1, name: 'John Doe' },
+  { id: 2, name: 'Jane Doe' }
+])
+```
+
+The `insert` method will "normalize" the given data. That means if you pass an object that contains any nested relationships, those relationships are also updated. Please see [Relationships: Getting Started](../relationships/getting-started.md#inserting-relationships) for more details about data normalization.
+
+Because the `insert` method might insert records of multiple models, it will always return a collection of entities that have been updated.
+
+```js
+const entities = await store.$repo(User).insert({ id: 1, name: 'John Doe' })
+
+/*
+  {
+    users: [
+      { id:1, name: 'Jane Doe' }
+    ]
+  }
+*/
+```
+
+## Inserting Data Without Normalization
+
+If you don't need the data to be normalized, you may use `add` method to insert data as well. The Biggest difference between `insert` method is that `add` method will always return the corresponding model instances rather than returning the whole `entities` object.
+
+```js
+const user = store.$repo(User).add({ id: 1, name: 'John Doe' })
+
+// { id: 1, name: 'John Doe' }
+```
+
+You may also pass an array of records to the `add` method. In that case, the returned value will be an array of models.
+
+```js
+const users = store.$repo(User).add([
+  { id: 1, name: 'John Doe' },
+  { id: 2, name: 'Jane Doe' }
+])
+
+/*
+  [
+    { id: 1, name: 'John Doe' },
+    { id: 2, name: 'Jane Doe' }
+  ]
+*/
+```
+
+## Inserting Data With Default Values
+
+When you pass an empty object or array to the `insert` or `add` method, it will do nothing. If you want to insert fresh data with all fields being default values, you may use `new` method. The `new` method will create a record with all fields filled with default values defined in the model.
+
+```js
+const user = store.$repo(User).new()
+
+// { id: '$uid1', name: '' }
+```
+
+::: warning
+Note that to be able to use `new` method, you must define the model's primary key field as `UID` type attribute, or else it will throw an error.
+:::
+
+## Replacing Whole Data
+
+When inserting data, you may use `fresh` method to replace whole existing records with the newly passed in data. It's pretty much equivalent to first delete all records, then inserting new data.
+
+```js
+// Existing records.
+[
+  { id: 1, name: 'John Doe' },
+  { id: 2, name: 'Jane Doe' }
+]
+
+// Replace whole records with the new data.
+store.$repo(User).fresh({ id: 3, name: 'Johnny Doe' })
+
+// The result.
+[
+  { id: 3, name: 'Johnny Doe' }
+]
+```
+
+And of course, you may pass an array of records as well.
+
+```js
+store.$repo(User).fresh([
+  { id: 3, name: 'Johnny Doe' },
+  { id: 4, name: 'Janie Doe' }
+])
+```
+
+Note that the `fresh` method will also normalize the given data. That means the returned value will always be an object on entities.
+
+```js
+const entities = await store.$repo(User).fresh({ id: 1, name: 'John Doe' })
+
+/*
+  {
+    users: [
+      { id:1, name: 'Jane Doe' }
+    ]
+  }
+*/
+```
+
+If you don't want the data to be normalized, you may use `replace` method, like `add` method for `insert` method.
+
+```js
+const user = store.$repo(User).replace({ id: 1, name: 'John Doe' })
+
+// { id: 1, name: 'John Doe' }
+```
+
+The `replace` method will also accept an array of records.
+
+```js
+const users = store.$repo(User).replace([
+  { id: 1, name: 'John Doe' },
+  { id: 2, name: 'Jane Doe' }
+])
+
+/*
+  [
+    { id: 1, name: 'John Doe' },
+    { id: 2, name: 'Jane Doe' }
+  ]
+*/
+```
+
+## Creating a model instance
+
+Sometimes, you may want to create a new model instance without actually storing the model to the store. In such a case, you may use `make` method to create a fresh model instance.
+
+```js
+const user = store.$repo(User).make()
+```
+
+You may also pass default values as an object.
+
+```tsx
+const user = store.$repo(User).make({
+  name: 'John Doe',
+  age: 30
+})
+```