我在mongo中有以下集合：
{
"_id" : ObjectId("506217890b50f300d020d237"),
"o_orderkey" : NumberLong(1),
"o_orderstatus" : "O",
"o_totalprice" : 173665.47,
"o_orderdate" : ISODate("1996-01-02T02:00:00Z"),
"o_orderpriority" : "5-LOW",
"o_clerk" : "Clerk#000000951",
"o_shippriority" : 0,
"o_comment" : "blithely final dolphins solve-- blithely blithe packages nag blith",
"customer" : {
"c_custkey" : NumberLong(36901),
"c_name" : "Customer#000036901",
"c_address" : "TBb1yDZcf 8Zepk7apFJ",
"c_phone" : "23-644-998-4944",
"c_acctbal" : 4809.84,
"c_mktsegment" : "AUTOMOBILE",
"c_comment" : "regular accounts after the blithely pending dependencies play blith",
"c_nationkey" : {
"n_nationkey" : NumberLong(13),
"n_name" : "JORDAN",
"n_comment" : "blithe, express deposits boost carefully busy accounts. furiously pending depos",
"n_regioin" : {
"r_regionkey" : NumberLong(4),
"r_name" : "MIDDLE EAST",
"r_comment" : "furiously unusual packages use carefully above the unusual, exp"
}
}
},
"o_lineitem" : [
{
"l_linenumber" : 1,
"l_quantity" : 17,
"l_extendedprice" : 21168.23,
"l_discount" : 0.04,
"l_tax" : 0.02,
"l_returnflag" : "N",
"l_linestatus" : "O",
"l_shipdate" : ISODate("1996-03-13T03:00:00Z"),
"l_commitdate" : ISODate("1996-02-12T03:00:00Z"),
"l_receiptdate" : ISODate("1996-03-22T03:00:00Z"),
"l_shipinstruct" : "DELIVER IN PERSON",
"l_shipmode" : "TRUCK",
"l_comment" : "blithely regular ideas caj",
"partsupp" : {
"ps_availqty" : 6157,
"ps_supplycost" : 719.17,
"ps_comment" : "blithely ironic packages haggle quickly silent platelets. silent packages must have to nod. slyly special theodolites along the blithely ironic packages nag above the furiously pending acc",
"ps_partkey" : {
"p_partkey" : NumberLong(155190),
"p_name" : "slate lavender tan lime lawn",
"p_mfgr" : "Manufacturer#4",
"p_brand" : "Brand#44",
"p_type" : "PROMO BRUSHED NICKEL",
"p_size" : 9,
"p_container" : "JUMBO JAR",
"p_retailprice" : 1245.19,
"p_comment" : "regular, final dol"
},
"ps_suppkey" : {
"s_suppkey" : NumberLong(7706),
"s_name" : "Supplier#000007706",
"s_address" : "BlHq75VoMNCoU380SGiS9fTWbGpeI",
"s_phone" : "33-481-218-6643",
"s_acctbal" : -379.71,
"s_comment" : "carefully pending ideas after the instructions are alongside of the dolphins. slyly pe",
"s_nationkey" : {
"n_nationkey" : NumberLong(23),
"n_name" : "UNITED KINGDOM",
"n_comment" : "fluffily regular pinto beans breach according to the ironic dolph",
"n_regioin" : {
"r_regionkey" : NumberLong(3),
"r_name" : "EUROPE",
"r_comment" : "special, bold deposits haggle foxes. platelet"
}
}
}
}
},
.
.
.
]
}
我试图翻译以下sql查询：
select
s_acctbal,
s_name,
n_name,
p_partkey,
p_mfgr,
s_address,
s_phone,
s_comment
from
part,
supplier,
partsupp,
nation,
region
where
p_partkey = ps_partkey
and s_suppkey = ps_suppkey
and p_size = 15
and p_type like '%BRASS'
and s_nationkey = n_nationkey
and n_regionkey = r_regionkey
and r_name = 'EUROPE'
and ps_supplycost = (
select
min(ps_supplycost)
from
partsupp, supplier,
nation, region
where
p_partkey = ps_partkey
and s_suppkey = ps_suppkey
and s_nationkey = n_nationkey
and n_regionkey = r_regionkey
and r_name = 'EUROPE'
)
order by
s_acctbal desc,
n_name,
s_name,
p_partkey;
我正在尝试的功能：
db.runCommand({
mapreduce: "ordersfull",
query: {
},
map: function Map() {
var pattern = /BRASS$/g;
for(var i in this.o_lineitem){
var p_size = this.o_lineitem[i].partsupp.ps_partkey.p_size;
var p_type = this.o_lineitem[i].partsupp.ps_partkey.p_type;
var region = this.o_lineitem[i].partsupp.ps_suppkey.s_nationkey.n_regioin.r_name;
if(p_size==15 && p_type.match(pattern)!=null && region == "EUROPE"){
emit("",{
s_acctbal: this.o_lineitem[i].partsupp.ps_suppkey.s_acctbal,
s_name: this.o_lineitem[i].partsupp.ps_suppkey.s_name,
n_name: this.o_lineitem[i].partsupp.ps_suppkey.s_nationkey.n_name,
p_partkey: this.o_lineitem[i].partsupp.ps_partkey.p_partkey,
p_mfgr: this.o_lineitem[i].partsupp.ps_partkey.p_mfgr,
s_address: this.o_lineitem[i].partsupp.ps_suppkey.s_address,
s_phone: this.o_lineitem[i].partsupp.ps_suppkey.s_phone,
s_comment: this.o_lineitem[i].partsupp.ps_suppkey.s_comment
} );
}
}
},
reduce: function(key, values) {
},
out: 'query002'
});
在我的结果中，我为所有条目获取了空值，会发生什么？
答案 0 :(得分：0)
您可以通过在JavaScript函数中包含print()或printjson()语句来调试MapReduce输出。生成的打印输出将保存在MongoDB日志中。
MapReduce有几个问题：
for .. in循环not work as you expect ..您应该使用array.forEach(..) array[index] emit()使用唯一的密钥名称reduce()应返回与发出数据结构相匹配的值query参数来限制需要检查的文档鉴于您似乎只是在不进行任何分组或reduce()的情况下迭代文档，您可能会发现在应用程序代码中获取文档并执行相同的匹配更容易。
在任何情况下，map()函数实际上应该更像：
var map = function () {
var pattern = /BRASS$/;
this.o_lineitem.forEach(function(item) {
var partKey = item.partsupp.ps_partkey;
var suppKey = item.partsupp.ps_suppkey;
var region = suppKey.s_nationkey.n_regioin.r_name;
if (partKey.p_size==15 && partKey.p_type.match(pattern) !=null && region == "EUROPE") {
emit(suppKey.s_name,
{
s_acctbal: suppKey.s_acctbal,
s_name: suppKey.s_name,
n_name: suppKey.s_nationkey.n_name,
p_partkey: partKey.p_partkey,
p_mfgr: partKey.p_mfgr,
s_address: suppKey.s_address,
s_phone: suppKey.s_phone,
s_comment: suppKey.s_comment
}
);
}
})
}
根据您的数据结构和所需的多重匹配和排序，将此查询转换为MongoDB 2.2中的新Aggregation Framework会更容易。
有一些current limitations需要注意（例如聚合管道输出的当前最大值为16MB），但您可能会发现查询更容易创建和调试。
以下是使用聚合框架的注释示例，包括订单状态，日期和感兴趣的部件/供应商项目的初始匹配条件：
db.ordersfull.aggregate(
// Find matching documents first (can take advantage of index)
{ $match: {
o_orderstatus: 'O',
o_orderdate: { $gte: new ISODate('2012-10-01') },
$and: [
{ o_lineitem: { $elemMatch: { 'partsupp.ps_partkey.p_size': 15 }} },
{ o_lineitem: { $elemMatch: { 'partsupp.ps_partkey.p_type': { $exists : true } }} },
{ o_lineitem: { $elemMatch: { 'partsupp.ps_suppkey.s_nationkey.n_regioin.r_name': 'EUROPE'}} }
]
}},
// Filter to fields of interest
{ $project: {
_id: 0,
o_lineitem: 1
}},
// Convert line item arrays into document stream
{ $unwind: '$o_lineitem' },
// Match desired line items
{ $match: {
'o_lineitem.partsupp.ps_partkey.p_size': 15,
'o_lineitem.partsupp.ps_partkey.p_type': /BRASS$/,
'o_lineitem.partsupp.ps_suppkey.s_nationkey.n_regioin.r_name': 'EUROPE'
}},
// Final field selection
{ $project: {
s_acctbal: '$o_lineitem.partsupp.ps_suppkey.s_acctbal',
s_name: '$o_lineitem.partsupp.ps_suppkey.s_name',
n_name: '$o_lineitem.partsupp.ps_suppkey.s_nationkey.n_name',
p_partkey: '$o_lineitem.partsupp.ps_partkey.p_partkey',
p_mfgr: '$o_lineitem.partsupp.ps_partkey.p_mfgr',
s_address: '$o_lineitem.partsupp.ps_suppkey.s_address',
s_phone: '$o_lineitem.partsupp.ps_suppkey.s_phone',
s_comment: '$o_lineitem.partsupp.ps_suppkey.s_comment'
}},
// Sort the output
{ $sort: {
s_acctbal: -1,
n_name: 1,
s_name: 1,
p_partkey: 1
}}
)