# CRUD

#### Create

To create new object there are several ways:

- create it passing arguments to `.create` method

```crystal
Contact.create(name: "John", age: 18)
```

- building it and saving manually

```crystal
c = Contact.new({:name => "Horus", :age => 4000})
c.age = 18
c.save
```

> Any `.create` and `#save` method call by default process under a transaction. If transaction is already started will not create new one.

To insert multiple records at once use `.import`:

```crystal
objects = [Contact.new({name: "Tom", age: 18}), Contact.new({name: "Jerry", age: 16})]
Contact.import(objects)
```

Other useful methods:

- `.find_or_create_by`
- `.find_or_create_by!`
- `.find_or_initialize_by`

#### Read

Object could be retrieved by id using `#find` (returns `T?`) and `#find!` (returns `T` or raises `RecordNotFound` exception) methods.

```crystal
Contact.find!(1) # #<Contact id: 1>
```

Also there is flexible DSL for building queries. To check out other supported methods see [query SQL](./query_dsl.md) section.

To reload all fields from db use `#reload`

```crystal
c1 = Contact.create(name: "Sam", age: 25)
Contact.where { _id == c1.id }.update(age: 30)
c1.reload
puts c1.age # 30
```

#### Update

There are several ways which allows to update object. Some of them were mentioned in mapping section. There are few extra methods to do this:
- `#update_column(name, value)` - sets directly attribute and store it to db without any callback
- `#update_columns(values)` - same for several ones
- `#set_attributes(values)` - just set attributes
- `#set_attribute(name, value)` - set attribute by given name

You can provide hash or named tuple with new field values to update all records satisfying given conditions:
```crystal
Contact.all.update(age: 1, name: "Wonder")
```

Will not trigger any callback.

Also relative modification allowed as well:

```crystal
# UPDATE contacts SET age = contacts.age + 2 WHERE contacts.id = 12
Contact.where { _id == 12 }.increment(age: 2)
# or
Contact.where { _id == 12 }.update { {:age => _age + 12} }
```

#### Destroy

To destroy object use `#delete` (is called without callbacks) or `#destroy`. To destroy several objects by their ids use class method:

```crystal
ids = [1, 20, 18]
Contact.destroy(ids)
Address.delete(1)
Country.delete([1, 2, 3])
```

To stop deleting from a callback just add some error:

```crystal
class MyModel < Jennifer::Model::Base
  # mapping

  before_destroy :check

  def check
    if some_field > 10
     errors.add(:some_field, "Can't be deleted")
    end
  end
end
```
> Any `#destroy` method call as well as `#save` use a transaction.

##### Truncation

To truncate entire table use:
```crystal
Jennifer::Adapter.default_adapter.truncate("contacts")
# or
Jennifer::Adapter.default_adapter.truncate(Contact)
```

This functionality could be useful to clear db between test cases.