Laravel Relationships Migration Schema

I’ve been having to look up relationship schemas too frequently and haven’t found a decent place that outlines them with migration and eloquent relationship declaration side by side. So if you’re looking for how to build a migration for (insert here) relationship, here it is.

*Based on Laravel 7

One to One

// Model A Migration
public function up()
    {
        Schema::table('A', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
        });
    }

// Model B Migration
public function up()
    {
        Schema::table('B', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
            $table->unsignedBigInteger('A_id');
            $table->foreign('A_id')->references('id')->on('A');
        });
    }

// A Model
public function b(){
    $this->hasOne(B::class);
}

// B Model
public function a(){
    $this->belongsTo(A::class);
}

One to Many

The migration looks the same as One to One, and similar in the Eloquent model. Just change ‘hasOne’ in the A class to ‘hasMany’

// Model A Migration
public function up()
    {
        Schema::table('A', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
        });
    }

// Model B Migration
public function up()
    {
        Schema::table('B', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
            $table->unsignedBigInteger('A_id');
            $table->foreign('A_id')->references('id')->on('A');
        });
    }

// A Model
public function b(){
    $this->hasMany(B::class);
}

// B Model
public function a(){
    $this->belongsTo(A::class);
}

Many to Many

Many to many relationships requires a third table called a pivot table that links the two.

// Model A Migration
public function up()
    {
        Schema::table('Amodel', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
        });
    }

// Model B Migration
public function up()
    {
        Schema::table('Bmodel', function (Blueprint $table) {
            $table->unsignedBigInteger('id');
        });
    }

// Pivot Table migration named A_B_table
// naming structure is important in Laravel, the model names are singular  
// and in alphabetical order
public function up()
    {
        Schema::table('A_B', function (Blueprint $table) {
            $table->unsignedBigInteger('A_id');
            $table->foreign('A_id')->references('id')->on('A');
            $table->unsignedBigInteger('B_id');
            $table->foreign('B_id')->references('id')->on('B');
        });
    }

// A Model
public function b(){
    $this->belongsToMany(B::class);
}

// B Model
public function a(){
    $this->belongsToMany(A::class);
}

Conclusion

Name	Migration	Eloquent Relationship
One to One A	id – integer	hasOne – b
One to One B	id – integer a_id – integer	belongsTo – a
One to Many A	id – integer	hasMany – b
One to Many B	id – integer a_id – integer	belongsTo – a
Many to Many A	id – integer	belongsToMany – b
Many to Many B	id – integer	belongsToMany – a
Many to Many Pivot	a_id – integer b_id – integer