关系数据库和nosql设计schema时的差别的例子

在关系数据库中和nosql的设计时,对于schema的设计是不同的.比如MYSQL中,设计如下一个例子:

mysql> select * from people;
+----+------------+
| id | name       |
+----+------------+
|  1 | Stephane   |
|  2 | John       |
|  3 | Michael    |
|  4 | Cinderella |
+----+------------+
mysql> select * from passports;
+----+-----------+---------+-------------+
| id | people_id | country | valid_until |
+----+-----------+---------+-------------+
|  4 |         1 | FR      | 2020-01-01  |
|  5 |         2 | US      | 2020-01-01  |
|  6 |         3 | RU      | 2020-01-01  |
+----+-----------+---------+-------------+

  这个如果要转换为mongodb要如何设计呢,首先一个方法是全部放在一个collection中,如

> db.people_all.find().pretty()
{
	"_id" : ObjectId("51f7be1cd6189a56c399d3bf"),
	"name" : "Stephane",
	"country" : "FR",
	"valid_until" : ISODate("2019-12-31T23:00:00Z")
}
{
	"_id" : ObjectId("51f7be3fd6189a56c399d3c0"),
	"name" : "John",
	"country" : "US",
	"valid_until" : ISODate("2019-12-31T23:00:00Z")
}
{
	"_id" : ObjectId("51f7be4dd6189a56c399d3c1"),
	"name" : "Michael",
	"country" : "RU",
	"valid_until" : ISODate("2019-12-31T23:00:00Z")
}
{ "_id" : ObjectId("51f7be5cd6189a56c399d3c2"), "name" : "Cinderella" }

  这样的话,如果要查询people的所有信息,放在同一个collection中是很快的,当然也可以分开两个collection进行嵌套,如:

> db.people_embed.find().pretty()
{
	"_id" : ObjectId("51f7c0048ded44d5ebb83774"),
	"name" : "Stephane",
	"passport" : {
		"country" : "FR",
		"valid_until" : ISODate("2019-12-31T23:00:00Z")
	}
}
{
	"_id" : ObjectId("51f7c70e8ded44d5ebb83775"),
	"name" : "John",
	"passport" : {
		"country" : "US",
		"valid_until" : ISODate("2019-12-31T23:00:00Z")
	}
}
{
	"_id" : ObjectId("51f7c71b8ded44d5ebb83776"),
	"name" : "Michael",
	"passport" : {
		"country" : "RU",
		"valid_until" : ISODate("2019-12-31T23:00:00Z")
	}
}
{ "_id" : ObjectId("51f7c7258ded44d5ebb83777"), "name" : "Cinderella" }

  甚至可以这样:

> db.passports_embed.find().pretty()
{
	"_id" : ObjectId("51f7c7e58ded44d5ebb8377b"),
	"country" : "FR",
	"valid_until" : ISODate("2019-12-31T23:00:00Z"),
	"person" : {
		"name" : "Stephane"
	}
}
{
	"_id" : ObjectId("51f7c7ec8ded44d5ebb8377c"),
	"country" : "US",
	"valid_until" : ISODate("2019-12-31T23:00:00Z"),
	"person" : {
		"name" : "John"
	}
}
{
	"_id" : ObjectId("51f7c7fa8ded44d5ebb8377d"),
	"country" : "RU",
	"valid_until" : ISODate("2019-12-31T23:00:00Z"),
	"person" : {
		"name" : "Michael"
	}
}
{
	"_id" : ObjectId("51f7c8058ded44d5ebb8377e"),
	"person" : {
		"name" : "Cinderella"
	}
}

  如果是大部分只查询people的本身信息的话,那么建议分开两个collection存放,避免每次把不需要加载的信息加载进去了.