Mongodb 的ORM框架 Morphia 之 Updating
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Introduction
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Updating (on the server)
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The Field Expression
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Samples initialization
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set/unset
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inc/dec
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add/All
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removeFirst/Last/All
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Multiple Operations
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updateFirst method
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update method
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createIfMissing (overload parameter)
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简介
这个有两个修改你的数据库的方法。你可以insert/save一个完整的实体，或者通过update操作。我们将在一下讨论。
Updating（On the server）
总之，当你通过Datesote调用update方法时就会向MongoDB服务器发送一个修改已存在数据的指令。
interface Datastore {
...
/** updates all entities found with the operations*/
UpdateResults update(Query query, UpdateOperations ops);
/** updates all entities found with the operations; if nothing is found insert the update as an entity if "createIfMissing" is true*/
UpdateResults update(Query query, UpdateOperations ops, boolean createIfMissing);
/** updates the first entity found with the operations*/
UpdateResults updateFirst(Query query, UpdateOperations ops);
/** updates the first entity found with the operations; if nothing is found insert the update as an entity if "createIfMissing" is true*/
UpdateResults updateFirst(Query query, UpdateOperations ops, boolean createIfMissing);
/** updates the first entity found with the operations; if nothing is found insert the update as an entity if "createIfMissing" is true*/
UpdateResults updateFirst(Query query, T entity, boolean createIfMissing);
}
public interface UpdateOperations {
/** sets the field value */
UpdateOperations set(String fieldExpr, Object value);
/** removes the field */
UpdateOperations unset(String fieldExpr);
/** adds the value to an array field*/
UpdateOperations add(String fieldExpr, Object value);
UpdateOperations add(String fieldExpr, Object value, boolean addDups);
/** adds the values to an array field*/
UpdateOperations addAll(String fieldExpr, List values, boolean addDups);
/** removes the first value from the array*/
UpdateOperations removeFirst(String fieldExpr);
/** removes the last value from the array*/
UpdateOperations removeLast(String fieldExpr);
/** removes the value from the array field*/
UpdateOperations removeAll(String fieldExpr, Object value);
/** removes the values from the array field*/
UpdateOperations removeAll(String fieldExpr, List values);
/** decrements the numeric field by 1*/
UpdateOperations dec(String fieldExpr);
/** increments the numeric field by 1*/
UpdateOperations inc(String fieldExpr);
/** increments the numeric field by value (negatives are allowed)*/
UpdateOperations inc(String fieldExpr, Number value);
}
The Field Expression
属性表达式是用在所有的操作上的，可以是单个的属性名，也可以是用点“.”连接的嵌套属性。在表达式中你也可以使用位置操作副($)。在属性
表达式中没有标准，你可以使用任何在MongoDB服务端有效符号。
事例初始化
一下所有的实例创建的连接和Morphia实例都使用的一下代码。
Morphia morphia = new Morphia();
morphia.map(Hotel.class).map(Address.class);
Datastore datastore = morphia.createDatastore("MorphiaSampleDb");
Hotel hotel = new Hotel("Fairmont", 3, new Address("1 Rideau Street", "Ottawa", "K1N8S7", "Canada"));
datastore.save(hotel);
UpdateOperations ops;
// This query will be used in the samples to restrict the update operations to only the hotel we just created.
// If this was not supplied, by default the update() operates on all documents in the collection.
// We could use any field here but _id will be unique and mongodb by default puts an index on the _id field so this should be fast!
Query updateQuery = datastore.createQuery(Hotel.class).field("_id").equal(hotel.getId());
// The Mapper class also provides a public static of the default _id field name for us...
Query updateQuery = datastore.createQuery(Hotel.class).field(Mapper.ID_KEY).equal(hotel.getId());
注意： 使用的是 equal() 而不是 equals()。
@Entity("hotels")
public class Hotel
{
@Id
private ObjectId id;
private String name;
private int stars;
@Embedded
private Address address;
@Embedded
List roomNumbers = new ArrayList();
// ... getters and setters
}
@Embedded
public class Address
{
private String street;
private String city;
private String postalCode;
private String country;
// ... getters and setters
}
set/unset
// 改变Hotel的name属性值
ops = datastore.createUpdateOperations(Hotel.class).set("name", "Fairmont Chateau Laurier");
datastore.update(updateQuery, ops);
//也可以操作嵌套文档， 改变address的city属性值ops = datastore.createUpdateOperations(Hotel.class).set("address.city", "Ottawa");datastore.update(updateQuery, ops);
// 删除Hotel的name属性值
// 当下会访问Hotel时name属性为null
ops = datastore.createUpdateOperations(Hotel.class).unset("name");
datastore.update(updateQuery, ops);
inc/dec
// 'stars'属性增长一
ops = datastore.createUpdateOperations(Hotel.class).inc("stars");
datastore.update(updateQuery, ops);
// 'stars'属性值增长4
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", 4);
datastore.update(updateQuery, ops);
// 'stars'属性值减少1
ops = datastore.createUpdateOperations(Hotel.class).dec("stars"); // 和 .inc("stars", -1) 相同
datastore.update(updateQuery, ops);
// 'stars'属性值减少4
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", -4);
datastore.update(updateQuery, ops);
add/All
// 把一个值放入到数组中 array() (+v 0.95)
// same as .add("roomNumbers", 11, false)
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 11);
datastore.update(updateQuery, ops); // [ 11 ]ops = datastore.createUpdateOperations(Hotel.class).set("roomNumbers", 11);
datastore.update(updateQuery, ops);
// 由于没有rooNumbers数组将会引起错误
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 11, false);
datastore.update(updateQuery, ops); // causes error
// 删除roomNummbers属性
ops = datastore.createUpdateOperations(Hotel.class).unset("roomNumbers");
datastore.update(updateQuery, ops);
// use the 3rd parameter to add duplicates
// add to end of array, same as add()
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 11, false);
datastore.update(updateQuery, ops); // [ 11 ]
// no change since its a duplicate... doesn't cause error
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 11, false);
datastore.update(updateQuery, ops); // [ 11 ]
// push onto the end of the array
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 12, false);
datastore.update(updateQuery, ops); // [ 11, 12 ]
// add even if its a duplicate
ops = datastore.createUpdateOperations(Hotel.class).add("roomNumbers", 11, true);
datastore.update(updateQuery, ops); // [ 11, 12, 11 ]removeFirst/Last/All
//given roomNumbers = [ 1, 2, 3 ]
ops = datastore.createUpdateOperations(Hotel.class).removeFirst("roomNumbers");
datastore.update(updateQuery, ops); // [ 2, 3 ]
//given roomNumbers = [ 1, 2, 3 ]
ops = datastore.createUpdateOperations(Hotel.class).removeLast("roomNumbers");
datastore.update(updateQuery, ops); // [ 1, 2 ]
ops = datastore.createUpdateOperations(Hotel.class).removeLast("roomNumbers");
datastore.update(updateQuery, ops); // [ 1 ]
ops = datastore.createUpdateOperations(Hotel.class).removeLast("roomNumbers");
datastore.update(updateQuery, ops); // [] empty array
//given roomNumbers = [ 1, 2, 3, 3 ]
ops = datastore.createUpdateOperations(Hotel.class).removeAll("roomNumbers", 3);
datastore.update(updateQuery, ops); // [ 1, 2 ]
//given roomNumbers = [ 1, 2, 3, 3 ]
ops = datastore.createUpdateOperations(Hotel.class).removeAll("roomNumbers", Arrays.asList(2, 3));
datastore.update(updateQuery, ops); // [ 1 ]Multiple Operations
你也可以在一个update指令中执行多个updae操作。
//设置城市名称为Ottawa和是stars的增长1
ops = datastore.createUpdateOperations(Hotel.class).set("city", "Ottawa").inc("stars");
datastore.update(updateQuery, ops);
//如果你在同一个属性上执行多次同样的指令操作，结果将会变化，即:只有最后一次有效
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", 50).inc("stars"); //stars只增长1
ops = datastore.createUpdateOperations(Hotel.class).inc("stars").inc("stars", 50); //stars只增长50
//你不能在同一个属性上执行相矛盾的操作。
ops = datastore.createUpdateOperations(Hotel.class).set("stars", 1).inc("stars", 50); //引起错误
{name: "Fairmont", stars: 5}, {name: "Last Chance", stars: 3}
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", 50);
// (+v 0.95 now takes into account the order())
// morphia 执行updateFirst方法仅仅执行第一个符合查询条件的数据项
datastore.updateFirst(datastore.find(Hotel.class).order("stars"), ops); //仅仅修改Last Chance
datastore.updateFirst(datastore.find(Hotel.class).order("-stars"), ops); // 仅仅修改 Fairmont//default shell version is to match first
//shell version has a multi to indicate to update all matches, not just first
//to mimic morphia operation, set multi = false
db.collection.update( criteria, objNew, upsert, multi );update 方法
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", 50);
// morphia 默认的update是修改所有的Hotels
datastore.update(datastore.createQuery(Hotel.class), ops); //所有的hotel都会增长//equivalent morphia shell version is... upsert = false, multi = true
db.collection.update( criteria, objNew, false, true );
所有的update都被重载支持一个"createIfMissing"参数。
ops = datastore.createUpdateOperations(Hotel.class).inc("stars", 50);
//修改， 如果没有找到就添加一个。
datastore.updateFirst(datastore.createQuery(Hotel.class).field("stars").greaterThan(100), ops, true);
// creates { "_id" : ObjectId("4c60629d2f1200000000161d"), "stars" : 50 }
//equivalent morphia shell version is... upsert = true
db.collection.update( criteria, objNew, true, multi );
原文连接：http://code.google.com/p/morphia/wiki/Updating