MongoDB：查询和投影操作符

原帖，请参看这里。

官网：https://docs.mongodb.com/manual/reference/operator/query/。

这一章节都是很简单的英语，就做一个很简单的备注，如果连这个英语都看不懂，那就需要提高了，程序员看不懂基本的英语是很难提高的。
这一章节还需要完善一些样例，这个有待补充。

查询选择器

比较

名字	描述
$eq	Matches values that are equal to a specified value.（判断相等）
$gt	Matches values that are greater than a specified value.（判断大于）
$gte	Matches values that are greater than or equal to a specified value.（判断大于等于）
$in	Matches any of the values specified in an array.（判断在其中）
$lt	Matches values that are less than a specified value.（判断小于）
$lte	Matches values that are less than or equal to a specified value.（判断小于等于）
$ne	Matches all values that are not equal to a specified value.（判断所有值都不等于指定值）
$nin	Matches none of the values specified in an array.（判断不在其中）

逻辑

名字	描述
$and	Joins query clauses with a logical AND returns all documents that match the conditions of both clauses.（与）
$not	Inverts the effect of a query expression and returns documents that do not match the query expression.（非）
$nor	Joins query clauses with a logical NOR returns all documents that fail to match both clauses.（异或）
$or	Joins query clauses with a logical OR returns all documents that match the conditions of either clause.（或）

元素

名字	描述
$exists	Matches documents that have the specified field.
$type	Selects documents if a field is of the specified type.

评估

名字	描述
$expr	Allows use of aggregation expressions within the query language.
$jsonSchema	Validate documents against the given JSON Schema.
$mod	Performs a modulo operation on the value of a field and selects documents with a specified result.
$regex	Selects documents where values match a specified regular expression.
$text	Performs text search.
$where	Matches documents that satisfy a JavaScript expression.

地理空间

名字	描述
$geoIntersects	Selects geometries that intersect with a GeoJSON geometry. The 2dsphere index supports $geoIntersects.
$geoWithin	Selects geometries within a bounding GeoJSON geometry. The 2dsphere and 2d indexes support $geoWithin.
$near	Returns geospatial objects in proximity to a point. Requires a geospatial index. The 2dsphere and 2d indexes support $near.
$nearSphere	Returns geospatial objects in proximity to a point on a sphere. Requires a geospatial index. The 2dsphere and 2d indexes support $nearSphere.

数组

名字	描述
$all	Matches arrays that contain all elements specified in the query.
$elemMatch	Selects documents if element in the array field matches all the specified $elemMatch conditions.
$size	Selects documents if the array field is a specified size.

位操作

名字	描述
$bitsAllClear	Matches numeric or binary values in which a set of bit positions all have a value of 0.
$bitsAllSet	Matches numeric or binary values in which a set of bit positions all have a value of 1.
$bitsAnyClear	Matches numeric or binary values in which any bit from a set of bit positions has a value of 0.
$bitsAnySet	Matches numeric or binary values in which any bit from a set of bit positions has a value of 1.

注释

名字	描述
$comment	Adds a comment to a query predicate.

投影操作

名字	描述
$	Projects the first element in an array that matches the query condition.
$elemMatch	Projects the first element in an array that matches the specified $elemMatch condition.
$meta	Projects the document’s score assigned during $text operation.
$slice	Limits the number of elements projected from an array. Supports skip and limit slices.