laravel-5.7: SQLSTATE[HY000]: General error: 1364 Field 'category_id' doesn't have a default value - laravel

Question

I'm new to Laravel and trying to add Product under Category but when I add Product then it shows this error:
SQLSTATE[HY000]: General error: 1364 Field 'category_id' doesn't have a default value (SQL: insert into products ..."
Initially i was adding these products without under any category than it was working and now its not adding under Category.
can anyone would prefer to provide me its solution?
here is my form:
<form enctype="multipart/form-data" class="form-horizontal" method="post" action="{{ url('admin/add-product') }}" name="add_product" id="add_product" novalidate="novalidate">{{ csrf_field() }}
<div class="control-group">
<label class="control-label">Under Category</label>
<div class="controls">
<select name="category_id" id="category_id" style="width:220px;">
<?php echo $categories_drop_down; ?>
</select>
</div>
</div>
<div class="control-group">
<label class="control-label">Product Name</label>
<div class="controls">
<input type="text" name="product_name" id="product_name">
</div>
</div>
<div class="uploader" id="uniform-undefined"><input name="image" id="image" type="file" size="19" style="opacity: 0;"><span class="filename">No file selected</span><span class="action">Choose File</span></div>
div class="form-actions">
<input type="submit" value="Add Product" class="btn btn-success">
</div>
</form>
here is ProductsController:
ProductsController.php
public function addProduct(Request $request)
{
if ($request->isMethod('post'))
{
$data = $request->all();
$product = new Product;
$product->product_name = $data['product_name'];
$product->product_code = $data['product_code'];
$product->product_color = $data['product_color'];
if ( ! empty($data['description']))
{
$product->description = $data['description'];
}
else
{
$product->description = '';
}
$product->price = $data['price'];
// Upload Image
if ($request->hasFile('image'))
{
$image_tmp = Input::file('image');
if ($image_tmp->isValid())
{
$extension = $image_tmp->getClientOriginalExtension();
$filename = rand(111, 99999) . '.' . $extension;
$large_image_path = 'images/backend_images/products/large/' . $filename;
$medium_image_path = 'images/backend_images/products/medium/' . $filename;
$small_image_path = 'images/backend_images/products/small/' . $filename;
// Resize Images
Image::make($image_tmp)->save($large_image_path);
Image::make($image_tmp)->resize(600, 600)->save($medium_image_path);
Image::make($image_tmp)->resize(300, 300)->save($small_image_path);
// Store image name in products table
$product->image = $filename;
}
}
$product->save();
/*return redirect()->back()->with('flash_message_success','Product has been added successfully!');*/
return redirect('/admin/view-products')->with('flash_message_success', 'Product has been added successfully!');
}
$categories = Category::where(['parent_id' => 0])->get();
$categories_drop_down = "<option value='' selected disabled>Select</option>";
foreach ($categories as $cat)
{
$categories_drop_down .= "<option value='" . $cat->id . "'>" . $cat->name . "</option>";
$sub_categories = Category::where(['parent_id' => $cat->id])->get();
foreach ($sub_categories as $sub_cat)
{
$categories_drop_down .= "<option value='" . $sub_cat->id . "'> -- " . $sub_cat->name . "</option>";
}
}
return view('admin.products.add_product')->with(compact('categories_drop_down'));
}

Answer 1

Although, there would be better ways to write this problem, the immediate solution would be to set the category_id field of your Product.
$product->product_name = $data['product_name'];
$product->product_code = $data['product_code'];
$product->product_color = $data['product_color'];
// Add this:
$product->category_id = $data['category_id'];

Answer 2

The main problem you have here is that in your migration you have category_id is not nullable which means it should have a value assigned to it from the controller you can either assign a value for it from your controller or you can go to your migration file and add this line
$table->integer('catagory_id')->nullable();
Then you will remigrate the table and it shouldn't throw this error again, but I prefer that you assign a value for it if you have relationship or something you want to connect it to it but if you don't have relationships then the entire category_id is useless in my point of view
If you want to assign a value to it, you should do something like this in your controller after the new product line:
$product->category_id = $request->input('category_id');
because your controller didn't take the value of the input which has the name of
category_id

Answer 3

As the error implies, it does not have a default value, you could solve it by either create a migration (or revise the one you had) so the column 'category_id' is nullable or just add the following line in the product creation:
$product->category_id = NULL;
You may find more information if needed about nullable at Laravel migration documentation