Mongoose 使用“填充”时执行多少个数据库查询?
有以下情况-Mongoose 使用“填充”时执行多少个数据库查询?,mongoose,mongoose-populate,Mongoose,Mongoose Populate,有以下情况- const Person = mongoose.model('Person', { name: String }); const FamilyTree = mongoose.model('FamilyTree', { person: { type: Schema.Types.ObjectId, ref: 'Person' }, children: [FamilyTree] }); const
const Person = mongoose.model('Person', {
name: String
});
const FamilyTree = mongoose.model('FamilyTree', {
person: { type: Schema.Types.ObjectId, ref: 'Person' },
children: [FamilyTree]
});
const run = async => {
await Promise.all(['Bob', 'Mike', 'Rory'].map( name => Person.create({name}) ));
let bob = await Person.find({name: 'Bob'}); // [request to BD] total requests = 1
let mike = await Person.find({name: 'Mike'}); // [request to BD] total requests = 2
let rory = await Person.find({name: 'Rory'}); // [request to BD] total requests = 3
await FamilyTree.create({
person: bob._id,
children: [
{
person: mike._id,
children: [
{
person: rory._id,
children: []
}
]
}
]
});
await FamilyTree.find().populate('person').exec(); // how many db requests will there be? 1 or 3?
}
如果响应包含以下数据,则使用“填充”时执行多少个数据库查询
从数据库中提取的数据-
{
person: {name: 'Bob'},
children: [{person: 'Mike', children: [{name: 'Rory', children: []}]}]
}
好问题,我也很好奇。然后我找到了这个 猫鼬在幕后做了一些聪明的事情。如果您查看作为这个填充查询的结果而进行的实际查询,它在幕后看起来会像这样
FamilyTree.find({});
person.find({ _id: { $in: ['5678', '9012', '3456'] } });
所以它只是一个$in
查询!Mongoose收集每个集合需要查找的所有_id字段,然后……我不太确定。看看源代码,它似乎做了一些聪明的事情来反映查询的结果,并根据其在传递到查询中的填充图中的位置,将正确的对象映射回每个原始文档……或者类似的东西(如果您愿意,您可以查看lib/model.js第2468行附近的源代码)
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