Tinydb 简明教程

TinyDB - Searching

TinyDB 提供了 search() 方法来帮助你从文档中检索任何数据。配合使用 query() 对象，search() 方法可用于在 JSON 文件中查找数据。有好多种方法可以在 TinyDB 数据库上使用 search() 方法。

Method 1: TinyDB search() with Existence of a Field

我们可以根据字段的存在情况从数据库中检索数据。我们通过一个例子来理解这一点。对于此示例以及其他示例，我们将使用以下 student 数据库。

[
   {
      "roll_number":1,
      "st_name":"elen",
      "mark":250,
      "subject":"TinyDB",
      "address":"delhi"
   },
   {
      "roll_number":2,
      "st_name":"Ram",
      "mark":[
         250,
         280
      ],
      "subject":[
         "TinyDB",
         "MySQL"
      ],
      "address":"delhi"
   },
   {
      "roll_number":3,
      "st_name":"kevin",
      "mark":[
         180,
         200
      ],
      "subject":[
         "oracle",
         "sql"
      ],
      "address":"keral"
   },
   {
      "roll_number":4,
      "st_name":"lakan",
      "mark":200,
      "subject":"MySQL",
      "address":"mumbai"
   },
   {
      "roll_number":5,
      "st_name":"karan",
      "mark":275,
      "subject":"TinyDB",
      "address":"benglore"
   }
]

Example

基于字段的存在情况进行的搜索查询如下所示 −

from tinydb import Query
student = Query()
db.search(student.address.exists())

上述查询会从 student 文件中检索以下数据 −

[
   {
      "roll_number":1,
      "st_name":"elen",
      "mark":250,
      "subject":"TinyDB",
      "address":"delhi"
   },
   {
      "roll_number":2,
      "st_name":"Ram",
      "mark":[
         250,
         280
      ],
      "subject":[
         "TinyDB",
         "MySQL"
      ],
      "address":"delhi"
   },
   {
      "roll_number":3,
      "st_name":"kevin",
      "mark":[
         180,
         200
      ],
      "subject":[
         "oracle",
         "sql"
      ],
      "address":"keral"
   },
   {
      "roll_number":4,
      "st_name":"lakan",
      "mark":200,
      "subject":"MySQL",
      "address":"mumbai"
   },
   {
      "roll_number":5,
      "st_name":"karan",
      "mark":275,
      "subject":"TinyDB",
      "address":"benglore"
   }
]

Method 2: TinyDB search() with Regular Expression

我们可以使用正则表达式 (Regex) 从数据库中检索特定的数据。我们通过几个示例来理解它是如何工作的。

Example 1

与正则表达式配对的完整项目搜索 −

from tinydb import Query
student = Query()
db.search(student.st_name.matches('[aZ]*'))

此查询会生成以下 output −

[
   {
      "roll_number":1,
      "st_name":"elen",
      "mark":250,
      "subject":"TinyDB",
      "address":"delhi"
   },
   {
      "roll_number":2,
      "st_name":"Ram",
      "mark":[
         250,
         280
      ],
      "subject":[
         "TinyDB",
         "MySQL"
      ],
      "address":"delhi"
   },
   {
      "roll_number":3,
      "st_name":"kevin",
      "mark":[
         180,
         200
      ],
      "subject":[
         "oracle",
         "sql"
      ],
      "address":"keral"
   },
   {
      "roll_number":4,
      "st_name":"lakan",
      "mark":200,
      "subject":"MySQL",
      "address":"mumbai"
   },
   {
      "roll_number":5,
      "st_name":"karan",
      "mark":275,
      "subject":"TinyDB",
      "address":"benglore"
   }
]

Example-2

区分大小写的正则表达式搜索 −

from tinydb import Query
import re
student = Query()
db.search(student.st_name.matches('lakan', flags=re.IGNORECASE))

它会生成以下 output −

[{
   'roll_number': 4,
   'st_name': 'lakan',
   'mark': 200,
   'subject': 'MySQL',
   'address': 'mumbai'
}]

Example-3

与正则表达式配对的项目部分 −

from tinydb import Query
student = Query()
db.search(student.st_name.search('r+'))

此查询会生成以下 output −

[{
   'roll_number': 5,
   'st_name': 'karan',
   'mark': 275,
   'subject': 'TinyDB',
   'address': 'benglore'
}]

Method 3: TinyDB search() using a Substring

在从 TinyDB 数据库中检索特定数据时，我们还可以使用子字符串。我们通过几个示例来理解它是如何工作的 −

Example-1

看一下此查询；它将获取 "address" 字段为 "delhi" 的所有行。

from tinydb import Query
student = Query()
db.search(student['address'] == 'delhi')

它将生成以下 output −

[
   {
      "roll_number":1,
      "st_name":"elen",
      "mark":250,
      "subject":"TinyDB",
      "address":"delhi"
   },
   {
      "roll_number":2,
      "st_name":"Ram",
      "mark":[
         250,
         280
      ],
      "subject":[
         "TinyDB",
         "MySQL"
      ],
      "address":"delhi"
   }
]

Example-2

在此查询中，我们对 search() 方法使用了稍微不同的语法。

from tinydb import Query
student = Query()
db.search(student.address.search('mumbai'))

它将获取 "address" 字段为 "mumbai" 的所有行。

[{
   'roll_number': 4,
   'st_name': 'lakan',
   'mark': 200,
   'subject': 'MySQL',
   'address': 'mumbai'
}]