Bienvenido a Desbordamiento de pila. Es una pregunta decente, publicaste. Permítame tener el privilegio de ayudarlo de la manera que pueda.
Este es un comando de agregación que se puede ejecutar en el shell mongo. Encuentre la explicación en línea.
db.collection.aggregate([
//match all those records which involve Wood.
{$match:{$or:[{"to":"wood"},{"from":"wood"}]}},
// sort all the messages by descending order
{$sort:{time:-1}},
{
// Now we need to group messages together, based on the to and from field.
// We generate a key - "last_message_between", with the value being a concatenation
// result of the values in to and from field.
// Now, Messages from Wood to billy and Billy to wood should be treated under a single group right.
// To achieve that, we do a small trick to make the result contain the name coming last
// alphabetically, first. So our key for all the Messages from Wood to Billy and Billy to Wood would be
// "Wood and Billy".
// And then we just display the first document that appears in the group, that would be the
// latest Message.
$group:{"_id":{
"last_message_between":{
$cond:[
{
$gt:[
{$substr:["$to",0,1]},
{$substr:["$from",0,1]}]
},
{$concat:["$to"," and ","$from"]},
{$concat:["$from"," and ","$to"]}
]
}
},"message":{$first:"$$ROOT"}
}
}
])
Puede ejecutar lo siguiente en mongoose.
Collection.aggregate(
{$match:{$or:[{"to":"wood"},{"from":"wood"}]}},
{$sort:{time:-1}},
{
$group:{"_id":{
"last_message_between":{
$cond:[
{
$gt:[
{$substr:["$to",0,1]},
{$substr:["$from",0,1]}]
},
{$concat:["$to"," and ","$from"]},
{$concat:["$from"," and ","$to"]}
]
}
},"message":{$first:"$$ROOT"}
}
},
function(err, res)
{
if (err) return handleError(err);
console.log(res);
}
)
