You should add the option `onDelete=&quot;SET NULL&quot;` in the annotation of your entity Publication like this:

&lt;!-- language: lang-php --&gt;

    class Publication
    {
        /**
        * @ORM\ManyToOne(targetEntity=&quot;Teacher&quot;, inversedBy=&quot;publications&quot;)
        * @ORM\JoinColumn(name=&quot;teacher_id&quot;, referencedColumnName=&quot;id&quot;, onDelete=&quot;SET NULL&quot;)
        */
        protected $teacher;
    }

Cheers!



I&#39;m using twitter bootstrap for some web app I&#39;m forced to do (I&#39;m not a web developer) and I can&#39;t find a way to disable the row lines for tables.

As you can see from the [Bootstrap documentation][1], the default table style contains line rows.

Regards,


  [1]: http://getbootstrap.com/components/#panels-tables

Remove row lines in twitter bootstrap

I am trying to load a csv file that has 14 columns like this:

    StartDate, var1, var2, var3, ..., var14

when I issue this command:

    systems &lt;- read.table(&quot;http://getfile.pl?test.csv&quot;, header = TRUE, sep = &quot;,&quot;)

I get an error message.
&gt; duplicate row.names are not allowed

It seems to me that the first column name is causing the issue. When I manually download the file and remove the `StartDate` name from the file, R successfully reads the file and replaces the first column name with `X`. Can someone tell me what is going on? The file is a (comma separated) csv file.

duplicate &#39;row.names&#39; are not allowed error

# The error
Cannot delete or update a parent row: a foreign key constraint fails.

# The classes

    class Teacher {

        /**
         *@ORM\OneToMany(targetEntity=&quot;publication&quot;, mappedBy=&quot;teacher&quot;)
         */
        protected $publications;
    }

    class Publication {

        /**
         * @ORM\ManyToOne(targetEntity=&quot;Teacher&quot;, inversedBy=&quot;publications&quot;)
         * @ORM\JoinColumn(name=&quot;teacher_id&quot;, referencedColumnName=&quot;id&quot;)
         */
        protected $teacher;
    }

# I want

What I want is to make it that when you delete a teacher, the id_teacher is modified to NULL. I want to keep the publication but without reference to Professor.

I don&#39;t know how do that in Doctrine, Is it possible? Or always the relationship has to be with a teacher?

Doctrine 2 OneToMany Cascade SET NULL

<h3 id="the-error"><a aria-hidden="true" tabindex="-1" href="#the-error"></a>The error</h3>
Cannot delete or update a parent row: a foreign key constraint fails.
<h3 id="the-classes"><a aria-hidden="true" tabindex="-1" href="#the-classes"></a>The classes</h3>
<pre><code class="hljs language-ini">class Teacher {

 /**
 *@ORM\OneToMany(targetEntity="publication", mappedBy="teacher")
 */
 protected $publications;
}

class Publication {

 /**
 * @ORM\ManyToOne(targetEntity="Teacher", inversedBy="publications")
 * @ORM\JoinColumn(name="teacher_id", referencedColumnName="id")
 */
 protected $teacher;
}
</code></pre>
<h3 id="i-want"><a aria-hidden="true" tabindex="-1" href="#i-want"></a>I want</h3>
What I want is to make it that when you delete a teacher, the id_teacher is modified to NULL. I want to keep the publication but without reference to Professor.
I don't know how do that in Doctrine, Is it possible? Or always the relationship has to be with a teacher?

Let&#39;s suppose I retrieve an entity `$e` and modify its state with setters:

    $e-&gt;setFoo(&#39;a&#39;);
    $e-&gt;setBar(&#39;b&#39;);

Is there any possibility to retrieve an array of fields that have been changed?

In case of my example I&#39;d like to retrieve `foo =&gt; a, bar =&gt; b` as a result

PS: yes, I know I can modify all the accessors and implement this feature manually, but I&#39;m looking for some handy way of doing this

Is there a built-in way to get all of the changed/updated fields in a Doctrine 2 entity

Let&#39;s say I have entity `$e`. Is there any generic way to store it as another row, which would have the same entity data but another primary key?

Why I need this: I&#39;m implementing some sort of [Temporal Database][1] schema and instead of updating the row I just need to create another one.


  [1]: http://en.wikipedia.org/wiki/Temporal_database

How to re-save the entity as another row in Doctrine 2

    WHERE a = 1 AND (b = 1 Or b = 2) AND (c = 1 OR c = 2)

How can i make this in Doctrine?

    $q-&gt;where(&quot;a = 1&quot;);
    $q-&gt;andWhere(&quot;b = 1&quot;)
    $q-&gt;orWhere(&quot;b = 2&quot;)
    $q-&gt;andWhere(&quot;c = 1&quot;)
    $q-&gt;orWhere(&quot;d = 2&quot;)

this isnt correctly... Should be:

    $q-&gt;where(&quot;a = 1&quot;);
    $q-&gt;andWhere(&quot;b = 1&quot;)
       $q-&gt;orWhere(&quot;b = 2&quot;)
    $q-&gt;andWhere(&quot;c = 1&quot;)
       $q-&gt;orWhere(&quot;d = 2&quot;)

but how can i make it? In Propel is function **getNewCriterion**, and in Doctrine...?

How to use andWhere and orWhere in Doctrine?

An `User` has one `Package` associated with it. Many users can refer to the same package. `User` cannot exists without a `Package` defined. `User` should own the relation. Relation is bidirectional, so a `Package` has zero or more users in it. 

These requirements lead to `ManyToOne` relation for `User` and `OneToMany` relation of `Package` in Doctrine 2. However `package_id` in `user` table (that is foreign-key) allows `null` values. I&#39;ve tried setting `nullable=false` but command:

     php app/console doctrine:generate:entities DL --path=&quot;src&quot; --no-backup

Says that there is no attribute `nullable` for the relation `ManyToOne`. **What i&#39;m missing?**

    class User
    {
    
        /**
         * @ORM\Id
         * @ORM\Column(type=&quot;integer&quot;)
         * @ORM\GeneratedValue(strategy=&quot;AUTO&quot;)
         */
        private $id;
    
        /**
         * @ORM\ManyToOne(targetEntity=&quot;Package&quot;, inversedBy=&quot;users&quot;)
         */
        private $package;
    
    }

    class Package
    {
    
        /**
         * @ORM\Id
         * @ORM\Column(type=&quot;integer&quot;)
         * @ORM\GeneratedValue(strategy=&quot;AUTO&quot;)
         */
        private $id;
    
        /**
         * @ORM\OneToMany(targetEntity=&quot;User&quot;, mappedBy=&quot;package&quot;)
         */
        private $users;
    
    }

Doctrine 2 can&#39;t use nullable=false in manyToOne relation?

What&#39;s the difference between `Doctrine\Common\Persistence\ObjectManager` and `Doctrine\ORM\EntityManager` when using it in a custom form type?

I can get the respository using both `$this-&gt;em-&gt;getRepository()` and `$this-&gt;om-&gt;getRepository()`.

    class MyFormType extends \Symfony\Component\Form\AbstractType
    {

        /**
         * @var Doctrine\ORM\EntityManager
         */
        protected $em;
    
        public function __construct(Doctrine\ORM\EntityManager $em)
        {
            $this-&gt;em = $em;
        }

     }

Instead of:

    class MyFormType extends \Symfony\Component\Form\AbstractType
    {

        /**
         * @var Doctrine\Common\Persistence\ObjectManager
         */
        protected $om;
    
        public function __construct(Doctrine\Common\Persistence\ObjectManager $om)
        {
            $this-&gt;om = $om;
        }

     }

Difference between ObjectManager and EntityManager in Symfony2?

I need to sort a PostgreSQL table ascending by a date/time field, e.g. `last_updated`.

But that field is allowed to be empty or null and I want records with null in `last_updated` come *before* non-null `last_updated`.  
Is this possible?

    order by last_updated asc  -- and null last_updated records first ??

Sort by column ASC, but NULL values first?

In my app there&#39;s a static variable that&#39;s being set to null when I return to my app from the external browser. Seems like the app or some portion of it is killed if the external web page I&#39;m launching is complex enough. 

If the app were to be killed entirely and then relauched from the main activity that would be ok, but the relaunch is from the activity that started the browser - and it&#39;s not meant to set the app state so it&#39;s crashing when accessing the null static variable. This is a one-out-of-six device problem for me so I need some advice.

Is there a flag to set to prevent this behavior?

static variable null when returning to the app

How do you replace a NULL value in the select with an empty string?
It doesn&#39;t look very professional to output &quot;NULL&quot; values.

This is very unusual and based on my syntax I would expect it to work.
I&#39;m hoping for an explanation why it doesn&#39;t.

    select CASE prereq WHEN (prereq IS NULL) THEN &quot; &quot; ELSE prereq end from test;

Example of what the original table looks like, what I want, and what actually prints:


    original     wanted      what actually prints
    --------     ------      ---------------------
    value1       value1      
    NULL                     NULL
    value2       value2      
    NULL                     NULL


As you can see it does the opposite of what I want, hence I tried flipping the IS NULL to IS NOT NULL and of course that didn&#39;t fix it. I also tried swapping the position of when case, which did not work.

It seems the 3 solutions given below all do the task.

    select if(prereq IS NULL ,&quot; &quot;,prereq ) from test
    select IFNULL(prereq,&quot;&quot;) from test
    select coalesce(prereq, &#39;&#39;) from test



MySql Query Replace NULL with Empty String in Select

&gt; **Possible Duplicate:**  
&gt; [what is &amp;ldquo;=null&amp;rdquo; and &amp;ldquo; IS NULL&amp;rdquo;](https://stackoverflow.com/questions/2749044/what-is-null-and-is-null)  
&gt; [Is there any difference between IS NULL and =NULL](https://stackoverflow.com/questions/3777230/is-there-any-difference-between-is-null-and-null)  

&lt;!-- End of automatically inserted text --&gt;

What is the difference between

    where x is null

and 

    where x = null

and why does the latter not work?

SQL is null and = null

I have the following code:

    return this.ObjectContext.BranchCostDetails.Where(
        b =&gt; b.TarrifId == tariffId &amp;&amp; b.Diameter == diameter
            || (b.TarrifId==tariffId &amp;&amp; !string.IsNullOrWhiteSpace(b.Diameter))
            || (!b.TarrifId.HasValue) &amp;&amp; b.Diameter==diameter);

And I get this error when I try to run the code:

&gt; LINQ to Entities does not recognize the method &#39;Boolean
&gt; IsNullOrWhiteSpace(System.String)&#39; method, and this method cannot be
&gt; translated into a store expression.&quot;

How can I solve this problem and write code better than this?

String.IsNullOrWhiteSpace in LINQ Expression

&gt; **Possible Duplicate:**  
&gt; [Efficiently finding the intersection of a variable number of sets of strings](https://stackoverflow.com/questions/2851938/efficiently-finding-the-intersection-of-a-variable-number-of-sets-of-strings)  

&lt;!-- End of automatically inserted text --&gt;

Say, have two Hashset, how to calculate the intersection of them?


    Set&lt;String&gt; s1 = new HashSet&lt;String&gt;();
    
    Set&lt;String&gt; s2 = new HashSet&lt;String&gt;();
    
    S1 INT S2 ?



How to calculate the intersection of two sets?

I&#39;d like to know if I can get the first element of a list or set.  Which method to use?

How to get the first element of the List or Set?

I am using this code to convert a `Set` to a `List`:

    Map&lt;String, List&lt;String&gt;&gt; mainMap = new HashMap&lt;&gt;();
    
    for (int i=0; i &lt; something.size(); i++) {
      Set&lt;String&gt; set = getSet(...); //returns different result each time
      List&lt;String&gt; listOfNames = new ArrayList&lt;&gt;(set);
      mainMap.put(differentKeyName, listOfNames);
    }

I want to avoid creating a new list in each iteration of the loop. Is that possible?

Convert Set to List without creating new List

The python wiki says: &quot;Membership testing with sets and dictionaries is much faster, O(1), than searching sequences, O(n). When testing &quot;a in b&quot;, b should be a set or dictionary instead of a list or tuple.&quot;

I&#39;ve been using sets in place of lists whenever speed is important in my code, but lately I&#39;ve been wondering why sets are so much faster than lists. Could anyone explain, or point me to a source that would explain, what exactly is going on behind the scenes in python to make sets faster?

What makes sets faster than lists?

I am trying to understand the Python `hash` function under the hood. I created a custom class where all instances return the same hash value. 

    class C:
        def __hash__(self):
            return 42

I just assumed that only one instance of the above class can be in a `dict` at any time, but in fact a `dict` can have multiple elements with the same hash.

    c, d = C(), C()
    x = {c: &#39;c&#39;, d: &#39;d&#39;}
    print(x)
    # {&lt;__main__.C object at 0x7f0824087b80&gt;: &#39;c&#39;, &lt;__main__.C object at 0x7f0823ae2d60&gt;: &#39;d&#39;}
    # note that the dict has 2 elements

I experimented a little more and found that if I override the `__eq__` method such that all the instances of the class compare equal, then the `dict` only allows one instance.

    class D:
        def __hash__(self):
            return 42
        def __eq__(self, other):
            return True

    p, q = D(), D()
    y = {p: &#39;p&#39;, q: &#39;q&#39;}
    print(y)
    # {&lt;__main__.D object at 0x7f0823a9af40&gt;: &#39;q&#39;}
    # note that the dict only has 1 element

So I am curious to know how a `dict` can have multiple elements with the same hash.

Why can a Python dict have multiple keys with the same hash?

I have the following two entities:

**1- PlayList:**

    @OneToMany(fetch = FetchType.EAGER, mappedBy = &quot;playlist&quot;, orphanRemoval = true, cascade =   CascadeType.ALL)
    @OrderBy(&quot;adOrder&quot;)
    private Set&lt;PlaylistadMap&gt; PlaylistadMaps = new HashSet&lt;PlaylistadMap&gt;(0);

- **CascadeType.ALL**: is needed for save and update on the PlaylistadMap collection when saving or updating the playlist entity.
- **orphanRemoval = true**: is needed when deleting the playlist entity, the PlaylistadMap references should be deleteed too.


**2- PlaylistadMap:**

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = &quot;fk_playlist&quot;, referencedColumnName = &quot;pkid&quot;, nullable = false)
    private Playlist playlist;

when deleting a playlist by using `getCurrentSession().delete();` i am getting the following exception:

    org.springframework.dao.InvalidDataAccessApiUsageException: deleted object would be re-saved by cascade (remove deleted object from associations): [com.xeno.advertisingsuite.web.domain.PlaylistadMap#6]; nested exception is org.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): [com.xeno.advertisingsuite.web.domain.PlaylistadMap#6]
    	at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:657)
    	at org.springframework.orm.hibernate3.HibernateTransactionManager.convertHibernateAccessException(HibernateTransactionManager.java:793)
    	at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:664)
    	at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:754)
    	at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:723)
    	at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:393)
    	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:120)
    	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    	at $Proxy54.deletePlayList(Unknown Source)
    	at com.xeno.advertisingsuite.web.beans.PlayListBean.deletePlaylist(PlayListBean.java:282)
    	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    	at java.lang.reflect.Method.invoke(Method.java:597)
    	at org.apache.el.parser.AstValue.invoke(AstValue.java:262)
    	at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:278)
    	at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
    	at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    	... 103 more
    Caused by: org.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): [com.xeno.advertisingsuite.web.domain.PlaylistadMap#6]
    	at org.hibernate.impl.SessionImpl.forceFlush(SessionImpl.java:1220)
    	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:188)
    	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:117)
    	at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
    	at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:677)
    	at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:669)
    	at org.hibernate.engine.CascadingAction$5.cascade(CascadingAction.java:252)
    	at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:392)
    	at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:335)
    	at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)
    	at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:425)
    	at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:362)
    	at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:338)
    	at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)
    	at org.hibernate.engine.Cascade.cascade(Cascade.java:161)
    	at org.hibernate.event.def.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:154)
    	at org.hibernate.event.def.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:145)
    	at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:88)
    	at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
    	at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1206)
    	at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:375)
    	at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
    	at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:656)

please advise how to fix this exception.

Deleted object would be re-saved by cascade (remove deleted object from associations)

I think I misunderstood the meaning of cascading in the context of a `@ManyToOne` relationship.

The case:

    public class User {
    
       @OneToMany(fetch = FetchType.EAGER)
       protected Set&lt;Address&gt; userAddresses;
    
    }
    
    public class Address {
    
       @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
       protected User addressOwner;
    
    }

What is the meaning of the `cascade = CascadeType.ALL`? For example, if I delete a certain address from the database, how does the fact that I added the `cascade = CascadeType.ALL` affect my data (the `User`, I guess)?

What is the meaning of the CascadeType.ALL for a @ManyToOne JPA association

I have three classes one of the names is User and this user has other classes instances. Like this;

    public class User{
        @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL)
    	public List&lt;APost&gt; aPosts;
    
    	@OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL)
    	public List&lt;BPost&gt; bPosts;
    }


 

       public class BPost extends Post {
        
        @ManyToOne(fetch=FetchType.LAZY) 	
        public User user;
     }
        
        public class APost extends Post {
        
         @ManyToOne(fetch=FetchType.LAZY) 
         public User user;
     }

it&#39;s working like this but generates empty tables in DB. Which have to contain foreign keys. When I tried to use `mappedBy` and `JoinColumn` annotations I got failed. How can I resolve this?

**Extra information:**

When I changed with;

     @ManyToOne(fetch=FetchType.LAZY)
     @JoinColumn(name=&quot;id&quot;)
     public User user;

and

     @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy=&quot;id&quot;)
     public List&lt;APost&gt; aPosts;

I&#39;m getting

A JPA error occurred (Unable to build EntityManagerFactory): Repeated column in mapping for entity: models.post.APost column: id (should be mapped with insert=&quot;false&quot; update=&quot;false&quot;)

**Final Edit:** Finally, I was totally wrong about JPA annotations. :( When I change

    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy=&quot;id&quot;)
    
to

    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy=&quot;user&quot;)
    
and

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name=&quot;user_id&quot;)

everything works ok. :)

JPA OneToMany and ManyToOne throw: Repeated column in mapping for entity column (should be mapped with insert=&quot;false&quot; update=&quot;false&quot;)

I am reading currently the documentation of Hibernate regarding the [entity associations][1] and I come accross a little difficulty to figure out some things. It has to do in essence with the difference between `ManyToOne` and `OneToMany` associations. Although I have used them in real projects, I cannot comprehend completely the difference between them. To my understanding, if a table / an entity has a `ManyToOne` association with another, then the association should be from the other side `OneToMany`. So, how should we decide which one to choose based on a specific case and how does it affect the database/queries/results? Is there everywhere a good example? 

P.S.: I reckon it would be helpful due to its relevance to the question, if someone could besides explain what is the point of the owner of the association and the difference between Bidirectional and Unidirectional association.   


  [1]: http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html/entity.html#entity-mapping-association

Hibernate/JPA ManyToOne vs OneToMany

I&#39;m working on forum template using Flask. When I attempt creating a new thread in the browser using forms, SQLAlchemy throws an AttributeError. The problem showed up when I tried implementing a one-to-many relationship with Forum-to-Thread and a one-to-many relationship with Thread-to-User.

models.py

    class User(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      username = db.Column(db.String(32), index=True, unique=True)
      password = db.Column(db.String(32), index=True)
      email = db.Column(db.String(120), index=True, unique=True)
      role = db.Column(db.SmallInteger, default=ROLE_USER)
    
      posts = db.relationship(&#39;Post&#39;, backref=&#39;author&#39;, lazy=&#39;dynamic&#39;)

    class Forum(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      title = db.Column(db.String(128))
      description = db.Column(db.Text)
    
      threads = db.relationship(&#39;Thread&#39;, backref=&#39;forum&#39;, lazy=&#39;dynamic&#39;)
    	  
    class Thread(db.Model):
      
      id = db.Column(db.Integer, primary_key=True)
      title = db.Column(db.String(128))
      author= db.Column(db.String(32))
      timestamp = db.Column(db.DateTime)
      forum_id = db.Column(db.Integer, db.ForeignKey(&#39;forum.id&#39;))
    
      posts = db.relationship(&#39;Post&#39;, backref=&#39;thread&#39;, lazy=&#39;dynamic&#39;)
    	
    class Post(db.Model):
      
      id = db.Column(db.Integer, primary_key=True)
      body = db.Column(db.Text)
      timestamp = db.Column(db.DateTime)
      thread_id = db.Column(db.Integer, db.ForeignKey(&#39;thread.id&#39;))
      user_id = db.Column(db.Integer, db.ForeignKey(&#39;user.id&#39;))

All the new posts/threads and handled within views.py

views.py

    @app.route(&#39;/forum/id=&lt;id&gt;/submit&#39;, methods=[&#39;GET&#39;,&#39;POST&#39;])
    @login_required
    def new_thread(id):
      form = ThreadForm()
      forum = Forum.query.filter_by(id=id).first()
      if form.validate_on_submit():
        thread = Thread(title=form.title.data,
                        author=g.user.username,
                        timestamp=datetime.utcnow())
        db.session.add(thread)
        db.session.flush()
        post = Post(body=form.body.data,
                    timestamp=datetime.utcnow(),
                    thread=thread.id,
                    author=g.user.id)
        db.session.add(post)
        db.session.commit()
        flash(&#39;Post successful.&#39;)
        return redirect(url_for(&#39;forum_index&#39;, id=id))
      return render_template(&#39;forum/thread_submit.html&#39;, title=forum.title, form=form) 

Content Type	Original Author	Original Content on Stackoverflow
Question	Nicolas Lino	View Question on Stackoverflow
Solution 1 - Doctrine	David Barreto	View Answer on Stackoverflow

Doctrine 2 OneToMany Cascade SET NULL

Doctrine Problem Overview

The error

The classes

I want

Doctrine Solutions

Solution 1 - Doctrine

duplicate 'row.names' are not allowed error

Remove row lines in twitter bootstrap

Attributions