Detailed explanation of ThinkPHP's M method example_PHP tutorial

M method is used to instantiate a basic model class. The difference between and D method is:

1. No need to customize model classes, reduce IO loading, and have better performance;
2. After instantiation, only methods in the basic model class (the default is the Model class) can be called;
3. You can specify the table prefix, database and database connection information during instantiation;
The power of the D method is reflected in how powerful the custom model class you encapsulate is. However, as the basic model class of the new version of the ThinkPHP framework becomes more and more powerful, the M method is becoming more and more practical than the D method.

M method calling format:

M('[Basic model name:]Model name','Data table prefix','Database connection information')

Let’s take a look at the specific uses of the M method:

1. Instantiate the basic model (Model) class

When no model is defined, we can use the following method to instantiate a model class for operation:

//实例化User模型
$User = M('User');
 //执行其他的数据操作
$User->select();

This method is the simplest and most efficient, because it does not need to define any model classes, so it supports cross-project calls. The disadvantage is also that there is no custom model class, so the relevant business logic cannot be written and only basic CURD operations can be completed.

$User = M('User');

is actually equivalent to:

$User = new Model('User');

means operating the think_user table. The M method also has a singleton function like the D method, and it will not be instantiated repeatedly if called multiple times. The model name parameter of the M method will be automatically converted to lowercase when converted into a data table, which means that ThinkPHP's data table naming specification is in an all-lowercase format.

2. Instantiate other public model classes

The first method of instantiation has no model class definition, so it is difficult to encapsulate some additional logic methods. However, in most cases, you may just need to extend some common logic, then you can try the following method.

$User = M('CommonModel:User');

The changed usage is actually equivalent to:

$User = new CommonModel('User');

Because the system's model classes can be automatically loaded, we do not need to manually import the class library before instantiation. The model class CommonModel must inherit Model. We can define some common logical methods in the CommonModel class, which eliminates the need to define specific model classes for each data table. If your project already has more than 100 data tables, most of them are basic For CURD operations, only some models have some complex business logic that needs to be encapsulated, so the combination of the first method and the second method is a good choice.

3. Incoming table prefix, database and other information

The M method has three parameters. The first parameter is the model name (can include basic model classes and databases), and the second parameter is used to set the prefix of the data table (leave it blank to take the table prefix of the current project configuration). The third parameter is used to set the currently used database connection information (leave it blank to take the database connection information configured by the current project), for example:

$User = M('db2.User','think_');

means instantiating the Model model class and operating the think_user table in the db2 database.
If the second parameter is left blank or not passed, it means using the data table prefix in the current project configuration. If the data table being operated does not have a table prefix, you can use:

$User = M('db1.User',null);

means instantiating the Model model class and operating the user table in the db1 database.
If the database you operate requires different user accounts, you can pass in the database connection information, for example:

$User = M('User','think_','mysql://user_a:1234@localhost:3306/thinkphp');

represents the basic model class using Model, then operates the think_user table, uses the user_a account to connect to the database, and the operating database is thinkphp.
The third connection information parameter can use DSN configuration or array configuration, and can even support configuration parameters.
For example, configured in the project configuration file:

'DB_CONFIG'=>'mysql://user_a:1234@localhost:3306/thinkphp';

then you can use:

$User = M('User','think_','DB_CONFIG');

Basic model classes and databases can be used together, for example:

$User = M('CommonModel:db2.User','think_');

If you want to instantiate a hierarchical model, using the public model class, we can use:

M('UserLogic:User');

to instantiate UserLogic, although this does not make much sense, because you can use

D('User','Logic');

Achieve the same function.