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Type:
Bug
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Resolution: Done
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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Hello everybody, according to the documentation it should be possible to set the readPreference as another key in the options object:
'use strict'; const { MongoClient, ReadPreference } = require('mongodb'); const assert = require('assert'); MongoClient.connect('mongodb://localhost:37017/testing') .then(db => { const map = function() { emit(this._id, this._id); }; const reduce = function(key, values) { return 123; }; return db.collection('items').mapReduce(map, reduce, { out: { inline: 1 }, readPreference: ReadPreference.SECONDARY_PREFERRED }) }) .then(console.log) .catch(console.error);
However I'm getting the following error when I try it:
{ MongoError: unknown m/r field for sharding: readPreference
at Function.MongoError.create (/private/tmp/tp-20170214102859/node_modules/mongodb-core/lib/error.js:31:11)
at /private/tmp/tp-20170214102859/node_modules/mongodb-core/lib/connection/pool.js:483:72
at authenticateStragglers (/private/tmp/tp-20170214102859/node_modules/mongodb-core/lib/connection/pool.js:429:16)
at Connection.messageHandler (/private/tmp/tp-20170214102859/node_modules/mongodb-core/lib/connection/pool.js:463:5)
at Socket.<anonymous> (/private/tmp/tp-20170214102859/node_modules/mongodb-core/lib/connection/connection.js:319:22)
at emitOne (events.js:96:13)
at Socket.emit (events.js:188:7)
at readableAddChunk (_stream_readable.js:176:18)
at Socket.Readable.push (_stream_readable.js:134:10)
at TCP.onread (net.js:551:20)
name: 'MongoError',
message: 'unknown m/r field for sharding: readPreference',
ok: 0,
errmsg: 'unknown m/r field for sharding: readPreference' }
The instance listening at localhost:37017 is a mongos running 3.2.12, the collection is sharded on "_id" (hashed) and the driver is 2.2.24.
While looking for a solution I noticed that in some code examples the readPreference option is instead passed embedded within the "out" option. If I do that, I won't get any errors and the query seems to work. However, I'm not sure if that option is not simply ignored there. How can I verify? Thank you for looking into this.