db.collection.explain()¶

Verbosity Modes冗长模式¶

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（详细）模式。

Explain and Write Operations解释并编写操作¶

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()返回有关将要执行的写操作的信息，但不会实际修改数据库。

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 $out stage. 从MongoDB 4.2开始，对于一个包含了$out阶段的聚合管道，你不能在executionStats模式或allPlainsExecution模式中运行explain命令/db.collection.explain()。Instead, you can either:但是，你可以：

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

explain() Mechanics机械化¶

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:与db.collection.find().explain()类似，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()构造允许查询修饰符的附加链接。For list of query modifiers, see db.collection.explain().find().help().有关查询修饰符列表，请参阅db.collection.explain().find().help()。
• The db.collection.explain().find() returns a cursor, which requires a call to .next(), or its alias .finish(), to return the explain() results. db.collection.explain().find()返回一个游标，需要调用.next()或其别名.finish()才能返回explain()结果。If run interactively in the mongo shell, the mongo shell automatically calls .finish() to return the results. 如果在mongo shell中以交互方式运行，mongo shell会自动调用.finish()以返回结果。For scripts, however, you must explicitly call .next(), or .finish(), to return the results. 但是，对于脚本，必须显式调用.next()或.finish()，才能返回结果。For list of cursor-related methods, see db.collection.explain().find().help().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，该游标允许查询修饰符的链接。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()以"queryPlanner"详细模式运行。

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. 以下示例以"allPlansExecution"详细模式运行db.collection.explain()。The db.collection.explain() returns the queryPlanner and executionStats for all considered plans for the specified update() operation:db.collection.explain()为指定的update()操作返回所有考虑的计划的queryPlanner和executionStats：

db.products.explain("allPlansExecution").update(
   { quantity: { $lt: 1000}, category: "apparel" },
   { $set: { reorder: true } }
)

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

db.collection.explain().find() construct allows for the chaining of query modifiers. 构造允许查询修饰符的链接。For example, the following operation provides information on the find() method with sort() and hint() query modifiers.例如，以下操作使用sort()和hint()查询修饰符提供有关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 in the mongo shell:有关可用查询修饰符的列表，请在mongo shell中运行：

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. 将游标返回到解释结果。If run interactively in the mongo shell, the mongo shell automatically iterates the cursor using the .next() method. 如果在mongo shell中以交互方式运行，mongo shell将使用.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()）以返回结果：

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