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4.8. 关于 HQL predicates

4.8. 关于 HQL predicates

predicates 形成 where 子句、包含 子句 和 搜索案例表达式的基础。它们是可解析为真实值的表达式，通常是 TRUE 或 FALSE，尽管涉及 NULL 值的布尔值比较通常解析为 UNKNOWN。

HQL 谓词

null Predicate

检查 null 值。可以应用到基本属性引用、实体引用和参数。HQL 还允许将它应用到组件/嵌入式类型。

示例：NULL Check

// select everyone with an associated address
select p
from Person p
where p.address is not null

// select everyone without an associated address
select p
from Person p
  where p.address is null

// select everyone with an associated address
select p
from Person p
where p.address is not null

// select everyone without an associated address
select p
from Person p
  where p.address is null

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像 Predicate

执行类似于字符串值的比较。语法为：

like_expression ::=
       string_expression
       [NOT] LIKE pattern_value
       [ESCAPE escape_character]

like_expression ::=
       string_expression
       [NOT] LIKE pattern_value
       [ESCAPE escape_character]

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语义遵循 SQL 等表达式的语义。pattern_value 是在 string _expression 中尝试匹配的模式。正如 SQL 一样，mod_value 可以使用 _ （下划线）和 %（百分比 ）作为通配符。含义相同。_ 匹配任何单个字符。% 匹配任意数量的字符。

可选的s cap_character 用于指定用于转义 pattern_value 中 _ 和 % 的特殊含义的转义字符。这在需要搜索模式（包括 _ 或 %） 时非常有用。

示例：LIKE Predicate

select p
from Person p
where p.name like '%Schmidt'

select p
from Person p
where p.name not like 'Jingleheimmer%'

// find any with name starting with "sp_"
select sp
from StoredProcedureMetadata sp
where sp.name like 'sp|_%' escape '|'

select p
from Person p
where p.name like '%Schmidt'

select p
from Person p
where p.name not like 'Jingleheimmer%'

// find any with name starting with "sp_"
select sp
from StoredProcedureMetadata sp
where sp.name like 'sp|_%' escape '|'

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Predicate 间

类似于 SQL BETWEEN 表达式。执行评估，说明值在 2 个其他值范围内。所有操作对象都应具有可比较类型。

示例：BETWEEN Predicate

select p
from Customer c
    join c.paymentHistory p
where c.id = 123
  and index(p) between 0 and 9

select c
from Customer c
where c.president.dateOfBirth
        between {d '1945-01-01'}
            and {d '1965-01-01'}

select o
from Order o
where o.total between 500 and 5000

select p
from Person p
where p.name between 'A' and 'E'

select p
from Customer c
    join c.paymentHistory p
where c.id = 123
  and index(p) between 0 and 9

select c
from Customer c
where c.president.dateOfBirth
        between {d '1945-01-01'}
            and {d '1965-01-01'}

select o
from Order o
where o.total between 500 and 5000

select p
from Person p
where p.name between 'A' and 'E'

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IN Predicate

IN predicate 执行检查特定值是否在值列表中。它的语法是：

in_expression ::= single_valued_expression
            [NOT] IN single_valued_list

single_valued_list ::= constructor_expression |
            (subquery) |
            collection_valued_input_parameter

constructor_expression ::= (expression[, expression]*)

in_expression ::= single_valued_expression
            [NOT] IN single_valued_list

single_valued_list ::= constructor_expression |
            (subquery) |
            collection_valued_input_parameter

constructor_expression ::= (expression[, expression]*)

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single_valued_expression 的类型和 single _valued _list 中的单个值 必须一致。Jakarta Persistence 查询语言将此处的有效类型限制为字符串、数字、日期、时间、时间戳和枚举类型。在 Jakarta Persistence 查询语言中，single_valued_expression 只能 指：

"状态字段"，这是简单属性的术语。特别是，这不包括关联和组件/嵌入式属性。

实体类型表达式.

在 HQL 中，single_valued_expression 可以指 一组更广泛的表达式类型。允许单值关联。同样是组件/嵌入式属性，尽管该功能取决于底层数据库中对元或"行值构造器语法"的支持级别。此外，HQL 不会以任何方式限制值类型，但应用开发人员应该意识到，不同的类型可能会基于底层数据库供应商获得有限的支持。这主要是 Jakarta Persistence 查询语言限制的原因。

值列表可能来自多个不同来源。在 constructor_expression 和 collection_valued_input_parameter 中，值列表不能为空；它必须至少包含一个值。

示例：IN Predicate

select p
from Payment p
where type(p) in (CreditCardPayment, WireTransferPayment)

select c
from Customer c
where c.hqAddress.state in ('TX', 'OK', 'LA', 'NM')

select c
from Customer c
where c.hqAddress.state in ?

select c
from Customer c
where c.hqAddress.state in (
    select dm.state
    from DeliveryMetadata dm
    where dm.salesTax is not null
)

// Not Jakarta Persistence query language compliant!
select c
from Customer c
where c.name in (
    ('John','Doe'),
    ('Jane','Doe')
)

// Not Jakarta Persistence query language compliant!
select c
from Customer c
where c.chiefExecutive in (
    select p
    from Person p
    where ...
)

select p
from Payment p
where type(p) in (CreditCardPayment, WireTransferPayment)

select c
from Customer c
where c.hqAddress.state in ('TX', 'OK', 'LA', 'NM')

select c
from Customer c
where c.hqAddress.state in ?

select c
from Customer c
where c.hqAddress.state in (
    select dm.state
    from DeliveryMetadata dm
    where dm.salesTax is not null
)

// Not Jakarta Persistence query language compliant!
select c
from Customer c
where c.name in (
    ('John','Doe'),
    ('Jane','Doe')
)

// Not Jakarta Persistence query language compliant!
select c
from Customer c
where c.chiefExecutive in (
    select p
    from Person p
    where ...
)

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4.8. 关于 HQL predicates

HQL 谓词

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