Tinydb 简明教程
TinyDB - Retrieve Data
有许多方法可以帮助您从 TinyDB 数据库中检索数据。但是要使用这些方法，您首先需要按如下所示创建 Query 类的实例 −
from tinydb import Query
Student = Query()此处， Student 是数据库的名称。
让我们探索从 TinyDB 数据库检索信息的各种方式。
Data Retrieval Using the Search() Method
search() 方法（顾名思义）返回与我们提供的查询匹配的项目列表，否则它将返回一个空列表。
对于此示例和其他示例，我们将使用以下 student 数据库数据 -
[
{
"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"
}
]让我们举一个 example 来理解 search() 方法 -
from tinydb import TinyDB, Query
db = TinyDB("leekha.json")
student = Query()
db.search(student.subject == 'TinyDB' )上述查询将从 student 数据库中检索以下 output -
[
{
"roll_number":1,
"st_name":"elen",
"mark":250,
"subject":"TinyDB",
"address":"delhi"
},
{
"roll_number":5,
"st_name":"karan",
"mark":275,
"subject":"TinyDB",
"address":"benglore"
}
]Data Retrieval Using the get() Method
与 search() 方法相反，get() 方法仅返回一个匹配的文档。否则，它将返回 None。例如，让我们采用以下代码 -
from tinydb import TinyDB, Query
student = Query()
db.get(student.subject == 'TinyDB' )上述查询将从 student 数据库中检索以下数据。
[{'roll_number': 1, 'st_name': 'elen', 'mark': 250, 'subject': 'TinyDB', 'address': 'delhi'}]Data Retrieval using the all() Method
all() 方法返回数据库中的所有文档。例如，
db.all()它将从 student 数据库中检索全部数据。
[
{
"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"
}
]