Tinydb 简明教程

TinyDB - The test() Query

test() 查询会测试给定参数是否与表中的数据匹配。如果它与数据匹配，它会返回已匹配的数据，否则它会返回一个空值。首先，我们需要定义一个 test 函数及其参数，然后它会搜索给定数据库中的项目。

The test() query will test if the given arguments match with the data in a table. If it matches with the data, it will return the matched data, otherwise it will return blank. First of all, we need to define a test function and its arguments and then it will search the item in a given database.

Syntax

TinyDB test() 的语法如下 -

The syntax of TinyDB test() is as follows −

db.search(Query().field.test(function or condition, *arguments))

此处， field 表示我们要访问的数据部分。 Query() 是对我们名为 student 的 JSON 表创建的对象。

Here, field represents the part of data that we want to access. Query() is the object created of our JSON table named student.

我们可以创建自定义测试函数，如下 -

We can create a custom test function as follows −

object = lambda t: t == 'value'

此处 lamba 关键字对于创建自定义测试函数很重要。

Here the lamba keyword is important to create the custom test function.

让我们借助几个例子来了解它是如何工作的。我们将使用我们在所有前一章中都曾使用过的相同的 student 数据库。

Let’s understand how it works with the help of a couple of examples. We will use the same student database that we have used in all the previous chapters.

Example 1

我们将首先创建一个测试函数，然后在我们的 student 表中使用它 -

We will first create a test function and then use it in our student table −

from tinydb import TinyDB, Query
db = TinyDB('student.json')
objects = lambda t: t == [250, 280]
db.search(Query().mark.test(objects))

它会提取其中 "mark" 字段具有值 [250, 280] 的行 -

It will fetch the rows where the "mark" field has the values [250, 280] −

[{'roll_number': 2, 'st_name': 'Ram', 'mark': [250, 280], 'subject':
['TinyDB', 'MySQL'], 'address': 'delhi'}]

Example 2

在此示例中，我们将在测试函数中使用 "subject" 字段 -

In this example, we will use the "subject" field in the test function −

student = Query()
db = TinyDB('student.json')
objects = lambda t: t == 'TinyDB'
db.search(student.subject.test(objects))

此查询会提取其中 "subject" 字段具有值 "TinyDB" 的所有行 -

This query will fetch all the rows where the "subject" field has the value "TinyDB" −

[
   {
      "roll_number":1,
      "st_name":"elen",
      "mark":250,
      "subject":"TinyDB",
      "address":"delhi"
   },
   {
      "roll_number":5,
      "st_name":"karan",
      "mark":275,
      "subject":"TinyDB",
      "address":"benglore"
   }
]