Examples to explain how to query connected table data in Laravel

Laravel is an open source PHP framework that is characterized by simplicity, elegance, and support for the MVC architecture. As one of the preferred tools for PHP developers, the Laravel framework is widely praised for its rapid development, excellent scalability, and excellent documentation support. Among them, Laravel's connection table query data is a very important function. Let's briefly introduce it below.

In the database, if there are relationships between different tables, we need to perform join queries based on these relationships to obtain the required data. This is a join table query. Below we will use examples to learn how to query connected table data in Laravel.

1. Create two data tables

Before writing the relevant code, we need to create two data tables in order to test the join table query function. Here, we take the student table and grade table as an example. The student table includes the student's student number, name, and class, and the grade table includes the student number, subject name, and grades. After creating the two data tables, you need to establish the corresponding Model in Laravel.

2. Query connected table data

Laravel query syntax is very concise and elegant, and it is also very convenient to use. Let's take a look at how to perform join table queries through Laravel.

We first define a method in the Student model to associate with the Grade model:

public function grades()
{
    return $this->hasMany('App\Grade', 'student_id', 'id');
}

The function of this method is to establish the relationship between the Student and Grade models, hasMany represents a Students may correspond to scores in multiple subjects, so a "one-to-many" relationship is used. The next two parameters are the database field names corresponding to Laravel. The first parameter represents the field name used to associate the student table in the grades table, and the second parameter represents the primary key of the student table.

Next, we can use Laravel's query method to query the data in the Student table and Grade table. Suppose we need to query the student's student ID number, name and grades of all subjects, we can write the following code:

$students = Student::with('grades')->get();

This code will return an array containing all student information and corresponding grades, so we need Use a foreach loop to traverse this array and output each student's name, student number, and grades for the corresponding subjects.

foreach ($students as $student) {
    echo $student->id . ' - ' . $student->name . '<br>';
    foreach ($student->grades as $score) {
        echo $score->grade . ' - ' . $score->subject . '<br>';
    }
}

This code will output the student number, name and grade information of all students. As can be seen from this example, it is very convenient to use Laravel to query data in connected tables, and the code size is very concise.

Summary

Laravel's connection table query data is very simple, elegant and convenient. You can easily establish relationships between different models by using Laravel's model association method. When using query statements, you only need to simply call the corresponding method to realize the query and output functions, which greatly reduces the difficulty and workload of coding. Proficient in Laravel's join table query function can greatly improve your development efficiency and bring more convenience to your development work.

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