createCriteria

用途

创建一个Grails的 HibernateCriteriaBuilder 实例，可用来构建Criteria查询。

举例

def c = Account.createCriteria()
def results = c.list {
	like("holderFirstName", "Fred%")
	and {
		between("balance", 500, 1000)
		eq("branch", "London")
	}
	maxResults(10)
	order("holderLastName", "desc")
}

描述

Criteria查询是用 Groovy builder 创建复杂查询的类型安全的先进方法，它比用StringBuffer强太多了。

详细用法可参考用户手册的Criteria章节，各种Criteria查询节点见下表：

Node	Description	Example
between	Where the property value is between to distinct values	between("balance", 500, 1000)
eq	Where a property equals a particular value	eq("branch", "London")
eqProperty	Where one property must equal another	eqProperty("lastTransaction","firstTransaction")
gt	Where a property is greater than a particular value	gt("balance",1000)
gtProperty	Where a one property must be greater than another	gtProperty("balance","overdraft")
ge	Where a property is greater than or equal to a particular value	ge("balance",1000)
geProperty	Where a one property must be greater than or equal to another	geProperty("balance","overdraft")
idEq	Where an objects id equals the specified value	idEq(1)
ilike	A case-insensitive 'like' expression	ilike("holderFirstName","Steph%")
in	Where a one property is contained within the specified list of values note: 'in' is a groovy reserve word, we must escape it by quotes.	'in'("holderAge",[18..65])
isEmpty	Where a collection property is empty	isEmpty("transactions")
isNotEmpty	Where a collection property is not empty	isNotEmpty("transactions")
isNull	Where a property is null	isNull("holderGender")
isNotNull	Where a property is not null	isNotNull("holderGender")
lt	Where a property is less than a particular value	lt("balance",1000)
ltProperty	Where a one property must be less than another	ltProperty("balance","overdraft")
le	Where a property is less than or equal to a particular value	le("balance",1000)
leProperty	Where a one property must be less than or equal to another	leProperty("balance","overdraft")
like	Equivalent to SQL like expression	like("holderFirstName","Steph%")
ne	Where a property does not equals a particular value	ne("branch", "London")
neProperty	Where one property does not equal another	neProperty("lastTransaction","firstTransaction")
order	Order the results by a particular property	order("holderLastName", "desc")
sizeEq	Where a collection property's size equals a particular value	sizeEq("transactions", 10)
sizeGt	Where a collection property's size is greater than a particular value	sizeGt("transactions", 10)
sizeGe	Where a collection property's size is greater than or equal to a particular value	sizeGe("transactions", 10)
sizeLt	Where a collection property's size is less than a particular value	sizeLt("transactions", 10)
sizeLe	Where a collection property's size is less than or equal to a particular value	sizeLe("transactions", 10)
sizeNe	Where a collection property's size is not equal to a particular value	sizeNe("transactions", 10)

Criteria还支持反射(projection)的概念，反射用来改变结果的自然结构。如下的查询用反射去统计有不同branch值的Account的数量：

def c = Account.createCriteria()
def branchCount = c.get {
	projections {
		countDistinct "branch"
	}
}

各种反射及其用法见下表简介：

Name	Description	Example
property	Returns the given property in the returned results	property("firstName")
distinct	Returns results using a single or collection of distinct property names	distinct("lastName") or distinct(['firstName', 'lastName'])
avg	Returns the average value of the given property	avg("age")
count	Returns the count of the given property name	count("branch")
countDistinct	Returns the distinct count of the given property name	countDistinct("branch")
groupProperty	Groups the results by the given property	groupProperty("lastName")
max	Returns the maximum value of the given property	max("age")
min	Returns the minimum value of the given property	min("age")
sum	Returns the sum of the given property	sum("balance")
rowCount	Returns count of the number of rows returned	rowCount()