更新Document
假设如下的JSON格式的数据已经保存到Mongodb中去了,现在要更新相关的数据。
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "type" : "vps" , "clients" : 1000}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
假设现在要将hosting中值为hostB的进行更新,则可以使用如下的方法:
BasicDBObject newDocument =new BasicDBObject();
newDocument.put("hosting", "hostB");
newDocument.put("type", "shared host");
newDocument.put("clients", 111);
collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);
newDocument.put("hosting", "hostB");
newDocument.put("type", "shared host");
newDocument.put("clients", 111);
collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);
可以看到,这里依然使用了BasicDBObject对象,并为其赋值了新的值后,然后使用collection的update方法,即可更新该对象。
更新后的输出如下:
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "type" : "vps" , "clients" : 1000}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "shared host" , "clients" : 111}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "shared host" , "clients" : 111}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
另外,还可以使用mongodb中的$inc修饰符号去对某个值进行更新,比如,要将hosting值为hostB的document的clients的值得更新为199(即100+99=199),可以这样:
BasicDBObject newDocument =new BasicDBObject().append("$inc",
new BasicDBObject().append("clients", 99));
collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);
new BasicDBObject().append("clients", 99));
collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);
则输出如下:
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "type" : "vps" , "clients" : 1000}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 199}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 199}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
接下来,讲解$set修饰符的使用。比如要把hosting中值为hostA的document中的
type的值进行修改,则可以如下实现:
BasicDBObject newDocument3 =new BasicDBObject().append("$set",
new BasicDBObject().append("type", "dedicated server"));
collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);
new BasicDBObject().append("type", "dedicated server"));
collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);
则输出如下,把type的值从vps改为dedicated server:
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "clients" : 1000 , "type" : "dedicated server"}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "clients" : 1000 , "type" : "dedicated server"}
要注意的是,如果不使用$set的修饰符,而只是如下代码:
BasicDBObject newDocument3 =new BasicDBObject().append("type", "dedicated server");
collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);
collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);
则会将所有的三个document的type类型都改为dedicated server了,因此要使用$set以更新特定的document的特定的值。
如果要更新多个document中相同的值,可以使用$multi,比如,要把所有vps为type的document,将它们的clients的值更新为888,可以如下实现:
BasicDBObject updateQuery =new BasicDBObject().append("$set",
new BasicDBObject().append("clients", "888"));
collection.update(new BasicDBObject().append("type", "vps"), updateQuery, false, true);
new BasicDBObject().append("clients", "888"));
collection.update(new BasicDBObject().append("type", "vps"), updateQuery, false, true);
输出如下:
{"_id" : {"$oid" : "x"} , "hosting" : "hostA" , "clients" : "888" , "type" : "vps"}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "clients" : "888" , "type" : "vps"}
{"_id" : {"$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id" : {"$oid" : "x"} , "hosting" : "hostC" , "clients" : "888" , "type" : "vps"}