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/**
* When a view is defined on a sharded collection, read of that view results in the following:
* 1) mongos executes the view read against the primary shard, agnostic to whether the read
* is on a view or an unsharded collection.
* 2) The primary shard resolves the view and on determining that the underlying collection is
* sharded, returns an 'CommandOnShardedViewNotSupportedOnMongod' error to mongos, with the
* resolved view definition attached.
* 3) mongos rewrites the query and resolved view definition to be an aggregate on the underlying
* collection and executes.
*
* This test confirms that this rewrite mechanism is only used when the underlying collection is
* sharded. If not sharded then the primary shard can perform the rewrite locally and execute
* without having to round-trip back to mongos.
*
* @tags: [
* ]
*/
(function() {
"use strict";
const st = new ShardingTest({shards: 1, rs: {nodes: 1}});
const dbName = "view_on_shard_rewrite";
const collName = "coll";
const viewName = "view";
const collNS = dbName + "." + collName;
const mongos = st.s0;
const configDB = mongos.getDB("config");
const mongosDB = mongos.getDB(dbName);
const shardPrimary = st.rs0.getPrimary();
const shardDB = shardPrimary.getDB(dbName);
assert.commandWorked(mongosDB.getCollection(collName).insert([{_id: 1}, {_id: 2}, {_id: 3}]));
assert.commandWorked(mongosDB.createView(viewName, collName, [{$addFields: {foo: "$_id"}}]));
function assertReadOnView(view) {
const result = view.find({}).sort({_id: 1}).toArray();
assert.eq(result, [{_id: 1, foo: 1}, {_id: 2, foo: 2}, {_id: 3, foo: 3}]);
}
// View read with unsharded collection works on both the primary shard and mongos.
assertReadOnView(mongosDB.getCollection(viewName));
assertReadOnView(shardDB.getCollection(viewName));
assert.commandWorked(configDB.adminCommand({enableSharding: dbName}));
// View read with unsharded collection works on both the primary shard and mongos, even when
// sharding has been enabled on the database.
assertReadOnView(mongosDB.getCollection(viewName));
assertReadOnView(shardDB.getCollection(viewName));
assert.commandWorked(configDB.adminCommand({shardCollection: collNS, key: {_id: 1}}));
// View read with sharded collection works on mongos.
assertReadOnView(mongosDB.getCollection(viewName));
// View read with sharded collection on the primary shard is rejected. This mimics what happens
// when mongos sends the equivalent read, with the caveat that mongos will use the view definition
// returned to rewrite the query and execute against the underlying collection.
assert.throwsWithCode(() => shardDB.getCollection(viewName).findOne({}),
ErrorCodes.CommandOnShardedViewNotSupportedOnMongod);
st.stop();
})();
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