查詢數(shù)組很容易诵冒，對于數(shù)組耕皮，我們可以這樣理解：數(shù)組中每一個(gè)元素都是這個(gè)鍵值對鍵的一個(gè)有效值境蜕，如下面的例子：我們要查詢出售apple的水果店:

db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("502251a309248743250688e1"), "name" : "good fruit", "fruits" : [ "banana", "pear", "orange" ] }{ "_id" : ObjectId("502251c109248743250688e2"), "name" : "good fruit", "fruits" : [ "banana", "apple", "tomato" ] }> db.fruitshop.find({"fruits":"apple"});{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("502251c109248743250688e2"), "name" : "good fruit", "fruits" : [ "banana", "apple", "tomato" ] }>
我們發(fā)現(xiàn)只要包含蘋果的數(shù)組都能被查詢出來。如果要通過多個(gè)元素來匹配數(shù)組凌停，就需要條件操作符"$all"粱年，比如我們要查詢既賣apple又賣banana的水果店：
db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("502251a309248743250688e1"), "name" : "good fruit", "fruits" : [ "banana", "pear", "orange" ] }{ "_id" : ObjectId("502251c109248743250688e2"), "name" : "good fruit", "fruits" : [ "banana", "apple", "tomato" ] }> db.fruitshop.find({"fruits":{"$all":["apple","banana"]}});{ "_id" : ObjectId("502251c109248743250688e2"), "name" : "good fruit", "fruits" : [ "banana", "apple", "tomato" ] }>
我們看，使用“$all”對數(shù)組內(nèi)元素的順序沒有要求罚拟，只要全部包含的數(shù)組都能查詢出來台诗。數(shù)組查詢也可以使用精確匹配的方式，即查詢條件文檔中鍵值對的值也是數(shù)組赐俗，如：
{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }{ "_id" : ObjectId("502253c109248743250688e5"), "name" : "good fruit", "fruits" : [ "apple", "orange", "pear", "banana" ] }> db.fruitshop.find({"fruits":["apple","orange","pear"]});{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }>
如果是精確匹配的方式拉队，MongoDB的處理方式是完全相同的匹配，即順序與數(shù)量都要一致秃励，上述中第一條文檔和查詢條件的順序不一致氏仗，第三條文檔比查詢條件文檔多一個(gè)元素，都沒有被匹配成功夺鲜！
對于數(shù)組的匹配皆尔，還有一種形式是精確指定數(shù)組中某個(gè)位置的元素匹配，我們前面提到币励，數(shù)組中的索引可以作為鍵使用慷蠕，如我們要匹配水果店售第二種水果是orange 的水果店：
db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }{ "_id" : ObjectId("502253c109248743250688e5"), "name" : "good fruit", "fruits" : [ "apple", "orange", "pear", "banana" ] }> db.fruitshop.find({"fruits.1":"orange"});{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }{ "_id" : ObjectId("502253c109248743250688e5"), "name" : "good fruit", "fruits" : [ "apple", "orange", "pear", "banana" ] }>
數(shù)組索引從0開始，我們匹配第二種水果就用furits.1作為鍵食呻。
"$size"條件操作符流炕，可以用來查詢特定長度的數(shù)組的，如我們要查詢賣3種水果的水果店：
db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }{ "_id" : ObjectId("502253c109248743250688e5"), "name" : "good fruit", "fruits" : [ "apple", "orange", "pear", "banana" ] }> db.fruitshop.find({"fruits":{"$size":3}});{ "_id" : ObjectId("5022518d09248743250688e0"), "name" : "big fruit", "fruits" : [ "apple", "pear", "orange" ] }{ "_id" : ObjectId("5022535109248743250688e4"), "name" : "fruit king", "fruits" : [ "apple", "orange", "pear" ] }>
但條件操作符"$size"不能和其他操作符連用如“$gt”等仅胞，這是這個(gè)操作符的一個(gè)缺陷每辟。使用這個(gè)操作符我們只能精確查詢某個(gè)長度的數(shù)組。如果實(shí)際中干旧，在查詢某個(gè)數(shù)組時(shí)渠欺，需要按其長度范圍進(jìn)行查詢，這里推薦的做法是：在這個(gè)文檔中額外增加一個(gè)“size”鍵椎眯，專門記錄其中數(shù)組的大小挠将，在對數(shù)組進(jìn)行"$push"操作同時(shí)胳岂，將這個(gè)“size”鍵值加1。如下所示：
db.fruitshop.find({"name":"big fruit"});{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "apple", "pear", "orange", "strawberry" ], "name" : "big fruit", "size" : 4 }> db.fruitshop.update({"name":"big fruit"},... {"$push":{"fruits":"banana"}, "$inc":{"size":1}}, false, false);> db.fruitshop.find({"name":"big fruit"});{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "apple", "pear", "orange", "strawberry", "banana" ], "name" : "big fruit", "size" : 5 }>
但這個(gè)方式和修改器"$addToSet"沒法配合使用舔稀，因?yàn)槟銦o法判斷這個(gè)元素是否添加到了數(shù)組中乳丰！
上篇提到了，find函數(shù)的第二個(gè)參數(shù)用于查詢返回哪些鍵内贮，他還可以控制查詢返回?cái)?shù)組的一個(gè)子數(shù)組产园，如下例：我只想查詢水果店售賣說過數(shù)組的前兩個(gè)：
db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "apple", "pear", "orange", "strawberry", "banana" ], "name" : "big fruit" }{ "_id" : ObjectId("5022535109248743250688e4"), "fruits" : [ "apple", "orange", "pear" ], "name" : "fruit king" }{ "_id" : ObjectId("502253c109248743250688e5"), "fruits" : [ "apple", "orange", "pear", "banana" ], "name" : "good fruit" }> db.fruitshop.find({}, {"fruits":{"$slice":2}});{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "apple", "pear" ], "name" : "big fruit" }{ "_id" : ObjectId("5022535109248743250688e4"), "fruits" : [ "apple", "orange" ], "name" : "fruit king" }{ "_id" : ObjectId("502253c109248743250688e5"), "fruits" : [ "apple", "orange" ], "name" : "good fruit" }>
“$slice”也可以從后面截取，用復(fù)數(shù)即可贺归，如-1表明截取最后一個(gè)淆两；還可以截取中間部分断箫，如[2,3]拂酣，即跳過前兩個(gè)，截取3個(gè)仲义，如果剩余不足3個(gè)婶熬，就全部返回！
db.fruitshop.find();{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "apple", "pear", "orange", "strawberry", "banana" ], "name" : "big fruit" }{ "_id" : ObjectId("5022535109248743250688e4"), "fruits" : [ "apple", "orange", "pear" ], "name" : "fruit king" }{ "_id" : ObjectId("502253c109248743250688e5"), "fruits" : [ "apple", "orange", "pear", "banana" ], "name" : "good fruit" }> db.fruitshop.find({}, {"fruits":{"$slice":-1}});{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "banana" ], "name" : "big fruit" }{ "_id" : ObjectId("5022535109248743250688e4"), "fruits" : [ "pear" ], "name" : "fruit king" }{ "_id" : ObjectId("502253c109248743250688e5"), "fruits" : [ "banana" ], "name" : "good fruit" }> db.fruitshop.find({}, {"fruits":{"$slice":[3,6]}});{ "_id" : ObjectId("5022518d09248743250688e0"), "fruits" : [ "strawberry", "banana" ], "name" : "big fruit" }{ "_id" : ObjectId("5022535109248743250688e4"), "fruits" : [ ], "name" : "fruit king" }{ "_id" : ObjectId("502253c109248743250688e5"), "fruits" : [ "banana" ], "name" : "good fruit" }>
如果第二個(gè)參數(shù)中有個(gè)鍵使用了條件操作符"$slice"埃撵，則默認(rèn)查詢會(huì)返回所有的鍵赵颅，如果此時(shí)你要忽略哪些鍵，可以手動(dòng)指明暂刘！如：
db.fruitshop.find({}, {"fruits":{"$slice":[3,6]}, "name":0, "_id":0});{ "fruits" : [ "strawberry", "banana" ] }{ "fruits" : [ ] }{ "fruits" : [ "banana" ] }>
【查詢內(nèi)嵌文檔】
查詢文檔有兩種方式饺谬，一種是完全匹查詢，另一種是針對鍵值對查詢谣拣！內(nèi)嵌文檔的完全匹配查詢和數(shù)組的完全匹配查詢一樣募寨，內(nèi)嵌文檔內(nèi)鍵值對的數(shù)量，順序都必須一致才會(huì)匹配森缠，如下例：
db.staff.find();{ "_id" : ObjectId("50225fc909248743250688e6"), "name" : { "first" : "joe", "middle" : "bush", "last" : "Schmoe" }, "age" : 45 }{ "_id" : ObjectId("50225fe209248743250688e7"), "name" : { "first" : "joe", "middle" : "bush" }, "age" : 35 }{ "_id" : ObjectId("50225fff09248743250688e8"), "name" : { "middle" : "bush", "first" : "joe" }, "age" : 25 }> db.staff.find({"name":{"first":"joe","middle":"bush"}});{ "_id" : ObjectId("50225fe209248743250688e7"), "name" : { "first" : "joe", "middle" : "bush" }, "age" : 35 }>
針對內(nèi)嵌文檔特定鍵值對的查詢是最常用的拔鹰！通過點(diǎn)表示法來精確表示內(nèi)嵌文檔的鍵：
db.staff.find();{ "_id" : ObjectId("50225fc909248743250688e6"), "name" : { "first" : "joe", "middle" : "bush", "last" : "Schmoe" }, "age" : 45 }{ "_id" : ObjectId("50225fe209248743250688e7"), "name" : { "first" : "joe", "middle" : "bush" }, "age" : 35 }{ "_id" : ObjectId("50225fff09248743250688e8"), "name" : { "middle" : "bush", "first" : "joe" }, "age" : 25 }> db.staff.find({"name.first":"joe", "name.middle":"bush"});{ "_id" : ObjectId("50225fc909248743250688e6"), "name" : { "first" : "joe", "middle" : "bush", "last" : "Schmoe" }, "age" : 45 }{ "_id" : ObjectId("50225fe209248743250688e7"), "name" : { "first" : "joe", "middle" : "bush" }, "age" : 35 }{ "_id" : ObjectId("50225fff09248743250688e8"), "name" : { "middle" : "bush", "first" : "joe" }, "age" : 25 }>
我們看，這樣查詢贵涵，所有有效文檔均被查詢到了列肢！通過點(diǎn)表示法，可以表示深入到內(nèi)嵌文檔內(nèi)部的鍵宾茂！利用“點(diǎn)表示法”來查詢內(nèi)嵌文檔瓷马，這也約束了在插入文檔時(shí)，任何鍵都不能包含“.” !!
當(dāng)內(nèi)嵌文檔變得復(fù)雜后跨晴，如鍵的值為內(nèi)嵌文檔的數(shù)組欧聘，這種內(nèi)嵌文檔的匹配需要一些技巧，如下例：
db.blogs.findOne();{ "_id" : ObjectId("502262ab09248743250688ea"), "content" : ".....", "comment" : [ { "author" : "joe", "score" : 3, "comment" : "just so so!" }, { "author" : "jimmy", "score" : 5, "comment" : "cool! good!" } ]}> db.blogs.find({"comment.author":"joe", "comment.score":{"$gte":5}});{ "_id" : ObjectId("502262ab09248743250688ea"), "content" : ".....", "comment" : [ { "author" : "joe", "score" : 3, "comment" : "just so so!" }, { "author" : "jimmy", "score" : 5, "comment" : "cool! good!" } ] }>
我們想要查詢評論中有叫“joe”并且其給出的分?jǐn)?shù)超過5分的blog文檔坟奥，但我們利用“點(diǎn)表示法”直接寫是有問題的树瞭，因?yàn)檫@條文檔有兩條評論拇厢，一條的作者名字叫“joe”但分?jǐn)?shù)只有3，一條作者名字叫“jimmy”晒喷，分?jǐn)?shù)卻給了5孝偎！也就是這條查詢條件和數(shù)組中不同的文檔進(jìn)行了匹配！這不是我們想要的凉敲，我們這里是要使用一組條件而不是單個(gè)指明每個(gè)鍵衣盾，使用條件操作符“$elemMatch”即可！他能將一組條件限定到數(shù)組中單條文檔的匹配上：
db.blogs.findOne();{ "_id" : ObjectId("502262ab09248743250688ea"), "content" : ".....", "comment" : [ { "author" : "joe", "score" : 3, "comment" : "just so so!" }, { "author" : "jimmy", "score" : 5, "comment" : "cool! good!" } ]}> db.blogs.find({"comment":{"$elemMatch":{"author":"joe", "score":{"$gte":5}}}});> db.blogs.find({"comment":{"$elemMatch":{"author":"joe", "score":{"$gte":3}}}});{ "_id" : ObjectId("502262ab09248743250688ea"), "content" : ".....", "comment" : [ { "author" : "joe", "score" : 3, "comment" : "just so so!" }, { "author" : "jimmy", "score" : 5, "comment" : "cool! good!" } ] }>
這樣做爷抓，結(jié)果是正確的势决！利用條件操作符“$elemMatch”可以組合一組條件，并且還能達(dá)到的“點(diǎn)表示法”的模糊查詢的效果蓝撇！
【$where】
上面提到的所有的鍵值對的查詢方式果复，我們也可以看出，已經(jīng)很強(qiáng)大了渤昌！但如果實(shí)際中真的遇到一種情況無法用上述方式實(shí)現(xiàn)時(shí)虽抄，不用慌，MongoDB為我們提供了終極武器："$where"独柑，用他可以執(zhí)行任意JavaScript作為查詢的一部分迈窟！最典型的應(yīng)用：一個(gè)文檔，如果有兩個(gè)鍵的值相等忌栅，就選出來车酣，否則不選：
db.fruitprice.find();{ "_id" : ObjectId("50226b4c3becfacce6a22a5b"), "apple" : 10, "banana" : 6, "pear" : 3 }{ "_id" : ObjectId("50226ba63becfacce6a22a5c"), "apple" : 10, "watermelon" : 3, "pear" : 3 }> db.fruitprice.find({"$where":function () {... for(var current in this){... for(var other in this){... if(current != other && this[current] == this[other]){... return true;... }... }... }... return false;... }});{ "_id" : ObjectId("50226ba63becfacce6a22a5c"), "apple" : 10, "watermelon" : 3, "pear" : 3 }>
我們可以看出，使用"$where"其實(shí)就是寫了一個(gè)javascript函數(shù)索绪，MongoDB在查詢時(shí)湖员，會(huì)將每個(gè)文檔轉(zhuǎn)換成一個(gè)javascript對象，然后扔到這個(gè)函數(shù)中去執(zhí)行者春，通過返回結(jié)果來判斷其是否匹配破衔！在實(shí)際使用中，盡量避免使用”$where" 條件操作符钱烟，因?yàn)槠湫阅芎懿钗福≡趫?zhí)行過程中，需要把每個(gè)檔案轉(zhuǎn)化為javascript對象拴袭！如果不可避免读第，則盡量這樣寫：find({”other“：”......“，......拥刻，“$where”:""})怜瞒，即將"$where"放最后，作為結(jié)果調(diào)優(yōu)，讓常規(guī)查詢作為前置過濾條件吴汪！這樣能減少一些性能損失惠窄！
我們這里還可以發(fā)現(xiàn)，“$where”條件操作符也是作為外層文檔的鍵使用漾橙，昨天說“$or”條件操作符是被作為外層文檔的鍵使用杆融。其余目前遇到的條件操作符都是被作為內(nèi)層文檔的鍵使用！