Detailed explanation of field method of ThinkPHP CURD method_PHP tutorial

The field method of the ThinkPHP CURD method is one of the coherent operation methods of the model. Its main purpose is to identify the field to be returned or operated , which can be used for query and write operations.

1. Used for query

The field method is the most frequently used in query operations.

$Model->field('id,title,content')->select();

The field method is used here to specify the values ​​of the three fields id, title, and content in the query result set. The SQL executed is equivalent to:

SELECT id,title,content FROM table

Of course, in addition to the select method, all query methods, including find, etc., can use the field method. Here we only use select as an example.
The above example can also be replaced by an array:

$Model->field(array('id','title','content'))->select();

The final executed SQL is equivalent to the above.

It seems that the usage of arrays is too complicated, but don’t draw this conclusion yet, you will understand the benefits of using arrays later.
The definition in array mode can define aliases for certain fields, for example:

$Model->field(array('id','title'=>'name','content'))->select();

The SQL executed is equivalent to:

SELECT id,title as name,content FROM table

If you wish to use it directly:

$Model->field('id,title as name,content')->select();

You may get incorrect results.
For some more complex field requirements, the advantages of arrays are more obvious, such as:

$Model->field(array('id','concat(name,'-',id)'=>'truename','LEFT(title,7)'=>'sub_title'))->select();

The SQL executed is equivalent to:

SELECT id,concat(name,'-',id) as truename,LEFT(title,7) as sub_title FROM table

I believe everyone understands that when you need to use SQL functions in fields, the array method can be a good solution.
Is the field method just that useful? If you think so, you are underestimating ThinkPHP's field method. ThinkPHP considers the details far more thoughtfully than you think.

Look at the following situation first. If there is a table with a lot of fields and two requirements, the first requirement is to get all the fields. This may be very simple, because the field method is not called or the empty field method is used directly. It can all be done, in fact, it is true:

$Model->select();
$Model->field()->select();
$Model->field('*')->select();

The above three usages are equivalent and are equivalent to executing SQL:

SELECT * FROM table

But this is not what I mean by getting all fields. I want to call all fields explicitly (for systems with high performance requirements, this requirement is not excessive, at least it is a better habit), then OK, Still very simple, the following usage can achieve the desired effect:

$Model->field(true)->select();

The usage of fied(true) will explicitly obtain the list of all fields in the data table, even if your data table has 100 fields.
The second requirement is that I want to get all field values ​​except the content field (the value of the text field is very memory-consuming). We can use the exclusion function of the field method . For example, the following method can be achieved Said function:

$Model->field('content',true)->select();

You can also exclude more fields:

$Model->field('user_id,content',true)->select();
 //或者用
$Model->field(array('user_id','content'),true)->select();

2. Used to write

In addition to query operations, the field method also has a very important security function - field legality detection (note: this function can only be supported starting from version 3.1). The field method combined with the create method can complete the field legality detection of form submission. If we use it in the processing method of form submission:

$Model->field('title,email,content')->create();

means that the only legal fields in the form are title, email and content fields. No matter how the user changes or adds the browser's submission field, it will be directly blocked. Since we don't want all other fields to be determined by user submissions, you can define additional fields to write through the autocomplete feature.

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