在MongoDB的列表查询中至少获得一个匹配项？
使用$in运算符至少获取一个匹配项。首先让我们创建一个包含文档的集合-
> db.atleastOneMatchDemo.insertOne({"StudentFavouriteSubject":["MySQL","MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2db5db64f4b851c3a13ce")
}
> db.atleastOneMatchDemo.insertOne({"StudentFavouriteSubject":["Java","C","MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2db71b64f4b851c3a13cf")
}
> db.atleastOneMatchDemo.insertOne({"StudentFavouriteSubject":["Python","C++","SQL Server"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2db87b64f4b851c3a13d0")
}
>db.atleastOneMatchDemo.insertOne({"StudentFavouriteSubject":["Ruby","Javascript","C#","MySQL"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd2dba9b64f4b851c3a13d1")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.atleastOneMatchDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd2db5db64f4b851c3a13ce"),
"StudentFavouriteSubject" : [
"MySQL",
"MongoDB"
]
}
{
"_id" : ObjectId("5cd2db71b64f4b851c3a13cf"),
"StudentFavouriteSubject" : [
"Java",
"C",
"MongoDB"
]
}
{
"_id" : ObjectId("5cd2db87b64f4b851c3a13d0"),
"StudentFavouriteSubject" : [
"Python",
"C++",
"SQL Server"
]
}
{
"_id" : ObjectId("5cd2dba9b64f4b851c3a13d1"),
"StudentFavouriteSubject" : [
"Ruby",
"Javascript",
"C#",
"MySQL"
]
}以下是获取至少一个匹配项的查询-
>db.atleastOneMatchDemo.find({"StudentFavouriteSubject":{"$in":["MongoDB","MySQL"]}}).pretty();这将产生以下输出-
{
"_id" : ObjectId("5cd2db5db64f4b851c3a13ce"),
"StudentFavouriteSubject" : [
"MySQL",
"MongoDB"
]
}
{
"_id" : ObjectId("5cd2db71b64f4b851c3a13cf"),
"StudentFavouriteSubject" : [
"Java",
"C",
"MongoDB"
]
}
{
"_id" : ObjectId("5cd2dba9b64f4b851c3a13d1"),
"StudentFavouriteSubject" : [
"Ruby",
"Javascript",
"C#",
"MySQL"
]
}