Combine two $or statements

问题:

I am trying to perform a query which is composed of two $or's:

|--------------------
| Date1  |  Date2   |
|--------------------
| NULL   |  NULL    | *
| NULL   |  TODAY   | *
| NULL   |  TOMRW   | 
| TODAY  |  TODAY   | *
| TODAY  |  NULL    | *
| TOMRW  |  NULL    | 
|--------------------

(I've marked the rows that would match with an asterisk)

(Date1 == null || Date1 <= today) && (Date2 == null || Date2 <= today)

I am not sure how to express this query in MongoDB.

It can be broken down into two individual queries that do exactly what they should:

{
    "$or": [{
        "Date1": {
            "$exists": false
        }
    },
    {
        "Date1": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")
        }
    }]
}

and

{
    "$or": [{
        "Date2": {
            "$exists": false
        }
    },
    {
        "Date2": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")
        }
    }]
}

Both of these select the correct set of documents - I just dont know how to execute them as a single query.

My initial thought was to do a query like this:

{
    $and: [orQuery1, orQuery2]
}

Using an $and query returns 0 results. It was explained why here in this thread: $and query returns no result

Also in that thread, a suggestion was made to do a query like this:

{
    Key: {valToMatch1: 1, valToMatch2: 2}
}

But I dont think an $or can be executed this way.

So, the question is: How do I construct my query such that I can combine the two $or's into a single query?

(Its getting very late so I hope this question makes sense.)

回答1:

use test
db.test.insert({a:1})
db.test.insert({a:2, Date2:new Date("01/07/2012")})
db.test.insert({a:3, Date2:new Date("01/08/2012")})
db.test.insert({a:4, Date1:new Date("01/07/2012"), Date2:new Date("01/07/2012")})
db.test.insert({a:5, Date1:new Date("01/07/2012")})
db.test.insert({a:6, Date1:new Date("01/08/2012")})

first subquery db.test.distinct('a', {...});

[1, 2, 3]

second subquery db.test.distinct('a', {...});

[ 1, 5, 6 ]

(Date1 == null || Date1 <= today) && (Date2 == null || Date2 <= today)

unwind

Date1 == null && Date2 == null ||
Date1 == null && Date2 <= today ||
Date1 <= today && Date2 == null ||
Date1 <= today && Date2 <= today ||

query

db.test.find(
{
  $or : 
  [
    {$and: [
        {"Date1": {"$exists": false}},
        {"Date2": {"$exists": false}}
      ]},
    {$and: [
        {"Date1": {"$exists": false}},
        {"Date2": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")}
        }
      ]},
    {$and: [
        {"Date2": {"$exists": false}},
        {"Date1": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")}
        }
      ]},
    {$and: [
        {"Date2": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")}
        },
        {"Date1": {
            "$exists": true,
            "$lte": new Date("2012-01-07T04:45:52.057Z")}
        }
      ]}
  ]
})
>[ 1 ]

this should work too (assume that 'not exist' and 'null' is the same)

db.test.find(
{
  $and : 
  [
    {$or: [
        {"Date1": null},
        {"Date1": { "$lte": new Date("2012-01-07T04:45:52.057Z")} }
      ]},
    {$or: [
        {"Date2": null},
        {"Date2": { "$lte": new Date("2012-01-07T04:45:52.057Z")} }
      ]}
  ]
}
)

回答2:

Actually, the problem lies not in the logic composition. Your nested $and $or query is perfectly fine.

It's the difference between MongoDB and JavaScript on creating a date that baffles you.

in Mongo:

> new Date("2012-01-07T04:45:52.057Z")
ISODate("0NaN-NaN-NaNTNaN:NaN:NaNZ")

in JavaScript:

> new Date("2012-01-07T04:45:52.057Z")
Sat, 07 Jan 2012 04:45:52 GMT

To fix it, you should use ISODate in mongo.

> ISODate('2012-01-07T04:45:52.057Z')
ISODate("2012-01-07T04:45:52.057Z")

UPDATE: append tests:

to prove the correctness of your logic combination, I wrote the following scripts:

populate.js: populate your sampling data:

var past = new Date('01/01/2011'),
    future = new Date('01/01/2013');

var dates = [
  {
    num: 1
  },
  {
    num: 2,
    Date2: past
  },
  {
    num: 3,
    Date2: future
  },
  {
    num: 4,
    Date1: past,
    Date2: past
  },
  {
    num: 5,
    Date1: past
  },
  {
    num: 6,
    Date1: future
  }
];

dates.forEach(function(date) {
  db.dates.insert(date);
});

query.js: test the three queries:

function queryNum(query) {
  print(db.dates.find(query).map(function(v) {
    return v.num;
  }));
}

var q1 = {
  "$or": [{
    "Date1": {
      "$exists": false
    }
  },
  {
    "Date1": {
      "$exists": true,
      "$lte": new Date('01/01/2012')
    }
  }]
};

var q2 = {
  "$or": [{
    "Date2": {
      "$exists": false
    }
  },
  {
    "Date2": {
      "$exists": true,
      "$lte": new Date('01/01/2012')
    }
  }]
};

var q3 = {
  $and: [q1, q2]
};

queryNum(q1);
queryNum(q2); 
queryNum(q3); 

It properly prints:

1,2,3,4,5
2,2,4,5,6
1,2,4,5