How to use multi-table query statements in thinkphp

With the development of the Internet, more and more applications need to perform multi-table queries on the database to achieve complex functional requirements. As an open source PHP development framework, thinkphp provides convenient and fast multi-table query statements. This article will introduce you to the implementation method of multi-table query in thinkphp.

1. Joined table query

Joint table query is also called a joint query. When a query obtains data from multiple tables, the query uses a join or union query. To use join table query in thinkphp, you need to use the join() method of Db class.

The parameters of the join() method are as follows:

$table: the name of the table to be connected

$join: the connection condition

$type: the connection type (Default is left join)

For example: If we now need to get the name field from table A and the status field from table B, connect the two tables based on the status field. It can be written like this:

Db::name('A')->alias('a')
     ->join('B b','a.status=b.status')
     ->field('a.name,b.status')
     ->select();

In this code, we use the join() method of the Db class to specify the table B to be connected and the connection condition a.status=b.status. It is important to note that we have set the alias a for table A here, because when obtaining the field status from table B, we need to use the table alias a to indicate which table's status field to obtain. Finally, we specify the field to be obtained through the field() method.

2. Multi-table correlation query

Multi-table correlation query refers to comparing the data of multiple tables during the query process and establishing correlation with a certain field. This requires to related queries. In thinkphp, there are three main methods of associated query: hasOne, hasMany and belongsToMany.

1.hasOne correlation query

hasOne is used for one-to-one correlation. By setting the corresponding relationship on the correlation fields of two tables, the data of the two tables can be connected according to certain rules. stand up. Let's look at an example:

class UserModel extends Model
{
    //hasOne关联查询
    public function order()
    {
        return $this->hasOne('OrderModel','user_id','id');
    }
}

In the above code, we use hasOne related query to query the situation of one user corresponding to one order. $this represents the current model, which is usually UserModel. The order() method is our custom method name, and the return value uses the hasOne method for related queries. Among them, 'OrderModel' refers to the model we want to query in association, and 'user_id' and 'id' respectively represent the associated fields between the two models.

2.hasMany correlation query

hasMany is used for one-to-many correlation. By setting the corresponding relationship on the correlation fields of two tables, the data of one table and multiple tables can be connected by certain rules. Let's look at an example:

class UserModel extends Model
{
    //hasMany关联查询
    public function order()
    {
        return $this->hasMany('OrderModel','user_id','id');
    }
}

In the above code, we use hasMany related query to query the situation of multiple orders corresponding to one user. $this represents the current model, the order() method is our custom method name, and the return value uses the hasMany method for related queries. Among them, 'OrderModel' refers to the model we want to query in association, and 'user_id' and 'id' respectively represent the associated fields between the two models.

3.belongsToMany related query

belongsToMany is used for many-to-many relationships. Corresponding relationships are set on the related fields of the intermediate tables, and the data of multiple tables can be connected according to certain rules. . Let’s look at an example:

class UserModel extends Model
{
    //belongsToMany关联查询
    public function goods()
    {
        return $this->belongsToMany('GoodsModel','user_goods','goods_id','user_id');
    }
}

In the above code, we use belongsToMany related query to query the situation of multiple users corresponding to multiple products. $this represents the current model, the goods() method is our custom method name, and the return value uses the belongsToMany method for related queries. Among them, 'GoodsModel' refers to the model we want to query in association, 'user_goods' refers to the name of the intermediate table, 'goods_id' and 'user_id' respectively represent the intermediate table and the associated fields between the two models.

3. Summary

This article mainly introduces the join table query and related query method based on Db class in thinkphp. During development, we often need to perform multi-table queries on the database. By studying the content of this article, I believe that we have mastered the corresponding basic knowledge. It is worth noting that the data table design should be reasonable to minimize data redundancy and improve query efficiency. Therefore, when performing multi-table queries, we should also follow this principle and split the data into multiple tables for processing as much as possible.

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