db.collection.explain()

Verbosity Modes详细模式

The behavior of db.collection.explain() and the amount of information returned depend on the verbosity mode.db.collection.explain()的行为和返回的信息量取决于verbosity模式。

Explain and Write Operations解释和编写操作

For write operations, db.collection.explain() returns information about the write operation that would be performed but does not actually modify the database.对于写操作，db.collection.explain()返回有关将要执行但实际上不会修改数据库的写操作的信息。

Restrictions限制

Starting in MongoDB 4.2, you cannot run the explain command/db.collection.explain() in executionStats mode or allPlansExecution mode for an aggregation pipeline that contains the $out stage. 从MongoDB 4.2开始，对于包含$out阶段的聚合管道，不能在executionStats模式或allPlansExecution模式下运行explain命令/db.collection.explain()。Instead, you can either:相反，您可以：

• run the explain in queryPlanner mode or在queryPlanner模式下运行解释，或者
• run the explain in executionStats mode or allPlansExecution mode but without the $out stage to return information for the stages that precede the $out stage.在executionStats模式或allPlansExecution模式下运行explain，但不包含$out阶段，以返回$out阶段之前的阶段的信息。

explain() Mechanics机械师

The db.collection.explain() method wraps the explain command and is the preferred way to run explain.db.collection.explain()方法包装explain命令，是运行explain的首选方法。

db.collection.explain().find() is similar to db.collection.find().explain() with the following key differences:类似于db.collection.find().explain()，但有以下关键区别：

• The db.collection.explain().find() construct allows for the additional chaining of query modifiers. db.collection.explain().find()构造允许额外的查询修饰符链接。For list of query modifiers, see db.collection.explain().find().help().有关查询修饰符的列表，请参阅db.collection.explain().find().help()。
• The db.collection.find().explain() returns a cursor, which requires a call to .next(), or its alias .finish(), to return the explain() results. db.collection.find().explain()返回一个游标，该游标需要调用.next()或其别名.finish()来返回explain()结果。If run interactively in mongosh, mongosh automatically calls .finish() to return the results. 如果在mongosh中以交互方式运行，mongosh会自动调用.finish()返回结果。For scripts, however, you must explicitly call .next(), or .finish(), to return the results. For list of cursor-related methods, see db.collection.explain().find().help().但是，对于脚本，必须显式调用.next()或.finish()才能返回结果。有关游标相关方法的列表，请参阅db.collection.explain().find().help()。

db.collection.explain().aggregate() is equivalent to passing the explain option to the db.collection.aggregate() method.相当于将explain选项传递给db.collection.aggregate()方法。

help()

To see the list of operations supported by db.collection.explain(), run:要查看db.collection.explain()支持的操作列表，请运行：

db.collection.explain().help()

db.collection.explain().find() returns a cursor, which allows for the chaining of query modifiers. 返回一个游标，该游标允许链接查询修饰符。To see the list of query modifiers supported by db.collection.explain().find() as well as cursor-related methods, run:要查看db.collection.explain().find()支持的查询修饰符列表以及与游标相关的方法，请运行：

db.collection.explain().find().help()

You can chain multiple modifiers to db.collection.explain().find(). 可以将多个修饰符链接到db.collection.explain().find()。For an example, see Explain find() with Modifiers.有关示例，请参阅使用修饰符解释find()。

queryPlanner Mode模式

By default, db.collection.explain() runs in "queryPlanner" verbosity mode.默认情况下，db.collection.explain()在"queryPlanner"详细模式下运行。

The following example runs db.collection.explain() in "queryPlanner" verbosity mode to return the query planning information for the specified count() operation:以下示例在"queryPlanner"详细模式下运行db.collection.explain()，以返回指定count()操作的查询计划信息：

db.products.explain().count( { quantity: { $gt: 50 } } )

executionStats Mode模式

The following example runs db.collection.explain() in "executionStats" verbosity mode to return the query planning and execution information for the specified find() operation:以下示例在"executionStats"详细模式下运行db.collection.explain()，以返回指定find()操作的查询计划和执行信息：

db.products.explain("executionStats").find(
   { quantity: { $gt: 50 }, category: "apparel" }
)

allPlansExecution Mode模式

The following example runs db.collection.explain() in "allPlansExecution" verbosity mode. 以下示例在"allPlansExecution"详细模式下运行db.collection.explain()。db.collection.explain() returns the queryPlanner and executionStats for all considered plans for the specified findAndModify() operation:db.collection.explain()为指定的findAndModify()操作返回所有考虑的计划的queryPlanner和executionStats：

db.products.explain( "allPlansExecution" ).findAndModify( {
   query: { name: "Tom", state: "active", rating: { $gt: 10 } },
   sort: { rating: 1 },
   update: { $inc: { score: 1 } }
} )

Explain find() with Modifiers用修饰符解释find()

db.collection.explain().find() construct allows for the chaining of query modifiers. 构造允许链接查询修饰符。For example, the following operation provides information on the find() method with sort() and hint() query modifiers.例如，以下操作提供了带有sort()和hint()查询修饰符的find()方法的信息。

db.products.explain("executionStats").find(
   { quantity: { $gt: 50 }, category: "apparel" }
).sort( { quantity: -1 } ).hint( { category: 1, quantity: -1 } )

For a list of query modifiers available, run the following in mongosh:有关可用查询修饰符的列表，请在mongosh中运行以下命令：

db.collection.explain().find().help()

Iterate the explain().find() Return Cursor迭代explain().find()返回游标

db.collection.explain().find() returns a cursor to the explain results. If run interactively in mongosh, mongosh automatically iterates the cursor using the .next() method. 将游标返回到解释结果。如果在mongosh中以交互方式运行，mongosh会使用.next()方法自动迭代游标。For scripts, however, you must explicitly call .next() (or its alias .finish()) to return the results:但是，对于脚本，必须显式调用.next()（或其别名.finish()）才能返回结果：

var explainResult = db.products.explain().find( { category: "apparel" } ).next();