Can anyone explain how to implement one-to-one, one-to-many and many-to-many relationships while designing tables with some examples?

How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?

I&#39;ve found the concept and meaning behind these methods to be a little confusing, is it possible for somebody to explain to me what the difference between `has` and `with` is, in the context of an example (if possible)?

Laravel - Eloquent &quot;Has&quot;, &quot;With&quot;, &quot;WhereHas&quot; - What do they mean?

I am looping over all comments posted by the Author of a particular post.

    foreach($post-&gt;user-&gt;comments as $comment)
	{
		echo &quot;&lt;li&gt;&quot; . $comment-&gt;title . &quot; (&quot; . $comment-&gt;post-&gt;id . &quot;)&lt;/li&gt;&quot;;
	}

This gives me

    I love this post (3)
    This is a comment (5)
    This is the second Comment (3)

How would I order by the post_id so that the above list is ordered as 3,3,5

Laravel orderBy on a relationship

I&#39;m developing a web API with Laravel 5.0 but I&#39;m not sure about a specific query I&#39;m trying to build.

My classes are as follows:

    
    class Event extends Model {
    
    	protected $table = &#39;events&#39;;
    	public $timestamps = false;
    
    	public function participants()
        {
            return $this-&gt;hasMany(&#39;App\Participant&#39;, &#39;IDEvent&#39;, &#39;ID&#39;);
        }
        
    	public function owner()
    	{
    		return $this-&gt;hasOne(&#39;App\User&#39;, &#39;ID&#39;, &#39;IDOwner&#39;);
    	}
    }

and


    class Participant extends Model {
    
    	protected $table = &#39;participants&#39;;
    	public $timestamps = false;
    
    	public function user()
        {
            return $this-&gt;belongTo(&#39;App\User&#39;, &#39;IDUser&#39;, &#39;ID&#39;);
        }
        
        public function event()
        {
        	return $this-&gt;belongTo(&#39;App\Event&#39;, &#39;IDEvent&#39;, &#39;ID&#39;);
        }
    }


Now, I want to get all the events with a specific participant.
I tried with:

    Event::with(&#39;participants&#39;)-&gt;where(&#39;IDUser&#39;, 1)-&gt;get();

but the `where` condition is applied on the `Event` and not on its `Participants`. The following gives me an exception:

    Participant::where(&#39;IDUser&#39;, 1)-&gt;event()-&gt;get();

I know that I can write this:

    $list = Participant::where(&#39;IDUser&#39;, 1)-&gt;get();
    for($item in $list) {
       $event = $item-&gt;event;
       // ... other code ...
    }

but it doesn&#39;t seem very efficient to send so many queries to the server.

What is the best way to perform a `where` through a model relationship using Laravel 5 and Eloquent?

Laravel where on relationship object

I&#39;m aware of the conceptual differences between Aggregation and Composition. Can someone tell me the implementation difference in Java between them with examples? 

Implementation difference between Aggregation and Composition in Java

Can anyone help me on how to save many to many relationship? I have tasks, user can have many tasks and task can have many users (many to many), What I want to achieve is that in *update form* admin can assign multiple users to specific task. This is done through html multiple select input 

    name=&quot;taskParticipants[]&quot;

 
The catch here is that through the same form (input) you can add/remove users, that&#39;s why I have to use sync().
Maybe I should start from the beginning but don&#39;t know where to start... 

**This is my User model:**

    public function tasks()
    {
        return $this-&gt;belongsToMany(&#39;Task&#39;,&#39;user_tasks&#39;);
    }

**Task model**

    public function taskParticipants()
    {
        return $this-&gt;belongsToMany(&#39;User&#39;,&#39;user_tasks&#39;);
    }

**TaskController**

    public function update($task_id)
    {
    	if (Input::has(&#39;taskParticipants&#39;))
    	{
    		foreach(Input::get(&#39;taskParticipants&#39;) as $worker)
    		{
    	       	$task2 = $task-&gt;taskParticipants-&gt;toArray();
    	       	$task2 = array_add($task2,$task_id,$worker);
    			$task-&gt;taskParticipants()-&gt;sync(array($task2));
    		}
    	}
    }

**This is structure of tables**
    tasks
    id|title|deadline
    
    user_tasks
    id|task_id|user_id



Laravel save / update many to many relationship

I know this question is asked by many people already&lt;br/&gt;
for my research, here&#39;s some questions asked before

 1. https://stackoverflow.com/questions/12899538/how-to-delete-all-relationships-in-neo4j-graph
 2. https://groups.google.com/forum/#!topic/neo4j/lgIaESPgUgE

But after all, still can&#39;t solve our problems,&lt;br/&gt;
we just want to delete &quot;ALL&quot; nodes and &quot;ALL&quot; relationships

![enter image description here][1]

suppose delete &quot;ALL&quot; can see there are left **0 nodes 0 properties and 0 relationships**

This is the screenshot i took after executing the delete &quot;ALL&quot; suggested by forum 

My question still the same, how do delete all nodes and all relationships in neo4j

  [1]: http://i.stack.imgur.com/ZuKFY.png

Delete all nodes and relationships in neo4j 1.8

What is the difference between `attach()` and `sync()` in Laravel 4&#39;s Eloquent ORM? I&#39;ve tried to look around but couldn&#39;t find anything!

Laravel Eloquent - Attach vs Sync

Any idea how to use an include with attributes (when you need to include only specific fields of the included table) with sequelize?

Currently I have this (but it doesn&#39;t work as expected):

    var attributes = [&#39;id&#39;, &#39;name&#39;, &#39;bar.version&#39;, [&#39;bar.last_modified&#39;, &#39;changed&#39;]];
    foo.findAll({
        where      : where,
        attributes : attributes,
        include    : [bar]
    }).success(function (result) { ...

How to use an include with attributes with sequelize?

What is the difference between these 2 relationships?

![enter image description here][1]

Edit: Also if you could provide a simple code example illustrating the difference, that would be really helpful!


  [1]: http://i.stack.imgur.com/sLFw1.png

UML relationships - dashed line vs solid line

In database design what do **n:m** and **1:n** mean? 

Does it have anything to do with keys or relationships?

Meaning of &quot;n:m&quot; and &quot;1:n&quot; in database design

In laravel, after using attach() or detach() to add or remove something from a relation, the collection has not changed. So if I have a model whose realation contains `[1, 2]`, after this:

    $model-&gt;relation()-&gt;detach(1);
    $model-&gt;relation()-&gt;attach(3);

it will still contain `[1, 2]`! How do I refresh it?

How do I reload a relation collection in laravel?

Is it possible to set up a double relationship in `activerecord` models via the `generate scaffold` command?

For example, if I had a `User` model and a `PrivateMessage` model, the private_messages table would need to keep track of both the `sender` and `recipient`.

Obviously, for a single relationship I would just do this:

    ruby script/generate scaffold pm title:string content:string user:references

Is there a similar way to set up two relations?

Also, is there anyway to set up aliases for the relations?

So rather than saying:

    @message.user

You can use something like:

  `@message.sender` or `@message.recipient`

Any advice would be greatly appreciated.

Thanks.

Ruby on rails - Reference the same model twice?

I&#39;m following the flask-sqlalchemy tutorial on [declaring models][1] regarding one-to-many relationship. The example code is as follows:

    class Person(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        name = db.Column(db.String(50))
        addresses = db.relationship(&#39;Address&#39;, backref=&#39;person&#39;,
                                    lazy=&#39;dynamic&#39;)
    
    class Address(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        email = db.Column(db.String(50))
        person_id = db.Column(db.Integer, db.ForeignKey(&#39;person.id&#39;))

Now I&#39;m wondering how to insert new records into DB using such model. I assume I need a constructor __init__, but I have difficulties to understand how it should be implemented and used. The main problem for me here is that Person depends on Address and Address has ForeignKey to Person, so it should know about the Person in advance.

Plase help me to understand how it should be performed.

Thank you in advance.

  [1]: http://flask-sqlalchemy.pocoo.org/2.1/models/

Inserting new records with one-to-many relationship in sqlalchemy

I have a ManyToOne relationship in one of my entities, like so:

    class License {
        // ...
        /**
         * Customer who owns the license
         * 
         * @var \ISE\LicenseManagerBundle\Entity\Customer
         * @ORM\ManyToOne(targetEntity=&quot;Customer&quot;, inversedBy=&quot;licenses&quot;)
         * @ORM\JoinColumn(name=&quot;customer_id&quot;, referencedColumnName=&quot;id&quot;)
         */
        private $customer;
        // ...
    }

    class Customer {
        // ...
        /**
         * Licenses that were at one point generated for the customer
         * 
         * @var \Doctrine\Common\Collections\ArrayCollection
         * @ORM\OneToMany(targetEntity=&quot;License&quot;, mappedBy=&quot;customer&quot;)
         */
        private $licenses;
        // ...
    }

This generates a database schema where the &quot;customer_id&quot; field of the license table is allowed to be null, which is exactly what I do not want.

Here&#39;s some code where I create a record to prove that it indeed allows null values for the reference fields:

    $em = $this-&gt;get(&#39;doctrine&#39;)-&gt;getEntityManager();
    $license = new License();
    // Set some fields - not the reference fields though
    $license-&gt;setValidUntil(new \DateTime(&quot;2012-12-31&quot;));
    $license-&gt;setCreatedAt(new \DateTime());
    // Persist the object
    $em-&gt;persist($license);
    $em-&gt;flush();

Basically, I don&#39;t want a License to be persisted without having a Customer assigned to it. Is there some annotation that needs to be set or should I just require a Customer object to be passed to my License&#39;s constructor?

The database engine I use is MySQL v5.1, and I am using Doctrine 2 in a Symfony2 application.

Doctrine 2 - Disallow null value on foreign keys of ManyToOne relationships

My `User` model has many `Target` and vice versa.
Now I&#39;ve got a given `User` and given `Target` and I want to access pivot data from their relation. The pivot column is called `type`

How can I achieve this?

Laravel: Get pivot data for specific many to many relation

While doing the HTML for my new template, I stumbled across a new meta tag

    &lt;link rel=&quot;profile&quot; href=&quot;http://gmpg.org/xfn/11&quot; /&gt;

What&#39;s this for? I found it linking to this [page][1], and through Google I found this [Microformat][2] but I didn&#39;t get it.


  [1]: http://gmpg.org/xfn/11
  [2]: http://microformats.org/wiki/rel-profile

All Relationship Solutions on Gang of Coders

Total of 17 Relationship Solutions