借用官网的例子数据：db.inventory
{ item: "journal", qty: 25, status: "A", size: { h: 14, w: 21, uom: "cm" }, tags: ["blank", "red"], dim_cm: [ 14, 21 ] }
{ item: "notebook", qty: 50, status: "A", size: { h: 8.5, w: 11, uom: "in" }, tags: ["red", "blank"], dim_cm: [ 14, 21 ] }
{ item: "paper", qty: 100, status: "D", size: { h: 8.5, w: 11, uom: "in" }, tags: ["red", "blank", "plain"], dim_cm: [ 14, 21 ] }
{ item: "planner", qty: 75, status: "D", size: { h: 22.85, w: 30, uom: "cm" }, tags: ["blank", "red"], dim_cm: [ 22.85, 30 ] }
{ item: "postcard", qty: 45, status: "A", size: { h: 10, w: 15.25, uom: "cm" }, tags: ["blue"], dim_cm: [ 10, 15.25 ] }查找所有：
db.inventory.find( {} )简单匹配普通属性：
db.inventory.find( { status: "D" } )使用操作符匹配普通属性：
db.inventory.find( { status: { $in: [ "A", "D" ] } } )多个属性匹配，之间是且的关系：
db.inventory.find( { status: "A", qty: { $lt: 30 } } )或的关系需要另加操作符：
db.inventory.find( { $or: [ { status: "A" }, { qty: { $lt: 30 } } ] } )且 和 或 共同使用的时：
db.inventory.find( {
status: "A",
$or: [ { qty: { $lt: 30 } }, { item: /^p/ } ] } )查找，数组/对象属性中有满足匹配的子项
db.inventory.find( { tags: "red" } )
db.inventory.find( { "size.uom": "in" } )数组/对象完全匹配查找（子项顺序必须完全相同，不然匹配不到）
db.inventory.find( { size: { h: 14, w: 21, uom: "cm" } } )
db.inventory.find( { tags: ["red", "blank"] } )匹配数组时注意：默认多元素子项可分摊匹配
db.inventory.find( { dim_cm: { $gt: 15, $lt: 20 } } )The following example queries for documents where the dim_cm array contains elements that in some combination satisfy the query conditions; e.g., one element can satisfy the greater than 15 condition and another element can satisfy the less than 20 condition, or a single element can satisfy both.
匹配数组：期望元素子项内匹配
db.inventory.find( { dim_cm: { $elemMatch: { $gt: 22, $lt: 30 } } } )The following example queries for documents where the dim_cm array contains at least one element that is both greater than ($gt) 22 and less than ($lt) 30.
匹配数组可以用索引（索引从0开始）
db.inventory.find( { "dim_cm.1": { $gt: 25 } } )匹配数组，可以多元素捆绑匹配
db.inventory.find( { tags: { $all: ["red", "blank"] } } )同（既包含’red’, 也包含’blank’的）：
db.inventory.find({ $and: [ { tags: "red" }, { tags: "blank" } ] })