SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: [ LARAVEL ]

I created a new database and added some foreign keys, cause I didn't this in my database before that and my whole webpage got's many issues.. thats why I decided to create a new one, with all the foreign keys I need.

Now I created a new user on my webpage and it works.. But If I'm trying to create a thread with this user, I'm getting this error message:

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SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (Laravel.threads, CONSTRAINT threads_ibfk_2 FOREIGN KEY (themen_id) REFERENCES themes (id)) (SQL: insert into threads (themen_id, thread, content, user_id, updated_at, created_at) values ({id}, unicorn, rainbows, 1, 2016-03-23 14:11:23, 2016-03-23 14:11:23))

---

and below this error, nearly the same error again:

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SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (Laravel.threads, CONSTRAINT threads_ibfk_2 FOREIGN KEY (themen_id) REFERENCES themes (id))

---

well, I don't haven't a single idea, what this means. I hope someone of you can help me there.

Thats how I created the table:

CREATE TABLE threads 
(
    id int AUTO_INCREMENT PRIMARY KEY,
    user_id int NOT NULL,
    themen_id int NOT NULL,
    thread varchar (120),
    content varchar (1200),
    created_at timestamp,
    updated_at timestamp,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (themen_id) REFERENCES themes(id)
);

CREATE TABLE comments 
(
    id int AUTO_INCREMENT PRIMARY KEY,
    thread_id int NOT NULL,
    user_id int NOT NULL,
    comment text,
    created_at timestamp,
    updated_at timestamp,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (thread_id) REFERENCES threads(id)
);

CREATE TABLE themes
(
    id int AUTO_INCREMENT PRIMARY KEY,
    thema text,
    created_at timestamp,
    updated_at timestamp    
);

CREATE TABLE users
(
    id int(10) PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255),
    email VARCHAR(255),
    password VARCHAR(60),
    remember_token VARCHAR(100),
    created_at timestamp,
    updated_at timestamp
);

I'm working with Laravel, of course I've changed the database name in the .env file. Well, I don't really now what to do right now.

Any help?

Thanks!

via Chebli Mohamed