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法律研究如何在 MongoDB 中搜索对象数组？
要搜索 MongoDB 中的对象数组，可以使用 $elemMatch 运算符。此运算符允许我们从数组对象中搜索多个组件。
为了理解上述概念，让我们 创建一个包含文档的集合。创建包含文档的集合的查询如下所示：
> db.searchArrayDemo.insertOne({"EmployeeFirstName":"Adam","EmployeeLastName":"Smith","EmployeeDateOfBirth":new ISODate("1992-01-31 13:45:10"), ... "EmployeeSkills":["Spring and Hibernate Framework","Machine Learning"], ... "EmployeeDetails":[ ... { ... "EmployeePerformanceArea":"Java", ... "Year":2001 ... }, ... { ... "EmployeePerformanceArea":"Python", ... "Year":2005 ... } ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5c77b3812386c62d05142a6a") } > db.searchArrayDemo.insertOne({"EmployeeFirstName":"Carol","EmployeeLastName":"Taylor", "EmployeeDateOfBirth":new ISODate("1993-04-21 11:10:20"), "EmployeeSkills":["C++","Cloud Computing"], "EmployeeDetails":[ { "EmployeePerformanceArea":"C++", "Year":1998 }, { "EmployeePerformanceArea":"C++ Game Developer", "Year":2007 } ] } ); { "acknowledged" : true, "insertedId" : ObjectId("5c77b58f2386c62d05142a6b") }
使用 find() 方法 显示集合中的所有文档。查询如下所示：
> db.searchArrayDemo.find().pretty();
以下是输出：
{
"_id" : ObjectId("5c77b3812386c62d05142a6a"),
"EmployeeFirstName" : "Adam",
"EmployeeLastName" : "Smith",
"EmployeeDateOfBirth" : ISODate("1992-01-31T13:45:10Z"),
"EmployeeSkills" : [
"Spring and Hibernate Framework",
"Machine Learning"
],
"EmployeeDetails" : [
{
"EmployeePerformanceArea" : "Java",
"Year" : 2001
},
{
"EmployeePerformanceArea" : "Python",
"Year" : 2005
}
]
}
{
"_id" : ObjectId("5c77b58f2386c62d05142a6b"),
"EmployeeFirstName" : "Carol",
"EmployeeLastName" : "Taylor",
"EmployeeDateOfBirth" : ISODate("1993-04-21T11:10:20Z"),
"EmployeeSkills" : [
"C++",
"Cloud Computing"
],
"EmployeeDetails" : [
{
"EmployeePerformanceArea" : "C++",
"Year" : 1998
},
{
"EmployeePerformanceArea" : "C++ Game Developer",
"Year" : 2007
}
]
}以下是 MongoDB 中搜索对象数组的查询。
情况 1
找到给定元素时。
查询如下所示：
> db.searchArrayDemo.find({EmployeeDetails:{$elemMatch:{EmployeePerformanceArea : "C++", Year : 1998}}}).pretty();
以下是输出：
{
"_id" : ObjectId("5c77b58f2386c62d05142a6b"),
"EmployeeFirstName" : "Carol",
"EmployeeLastName" : "Taylor",
"EmployeeDateOfBirth" : ISODate("1993-04-21T11:10:20Z"),
"EmployeeSkills" : [
"C++",
"Cloud Computing"
],
"EmployeeDetails" : [
{
"EmployeePerformanceArea" : "C++",
"Year" : 1998
},
{
"EmployeePerformanceArea" : "C++ Game Developer",
"Year" : 2007
}
]
}情况 2
找不到给定元素时。
查询如下所示：
> db.searchArrayDemo.find({EmployeeDetails:{$elemMatch:{EmployeePerformanceArea : "C", Year : 1996}}}).pretty();
当找不到给定元素时，您将不会获得任何结果。
更新于： 2023年9月10日
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