122 | Collections in JPQL and Criteria QueriesCollections may appear in JPQL queries: as parameters - when collections are assigned as arguments. as path expressions - in navigation to persistent collection fields. IS [NOT] EMPTY The IS [NOT ... of elements in a specified collection. For example: SIZE(c.languages) is evaluated to the number |
82 | Query Parameters in JPA. Named parameters can be easily identified in a query string by their special form, which is a colon ... are defined implicitly by appearing in the query string. The parameter type is inferred by the context. In ... multiple times in the query string. A query can be run only after setting values for all its parameters |
81 | Literals in JPQL and Criteria QueriesLiterals in JPQL, as in Java, represent constant values. JPQL supports various types of literals ... values. Literals should only be embedded in JPQL queries when a single constant value is always used and never replaced. The NULL literal The NULL literal represents a null value, similarly to null in |
81 | Locking in JPA in ObjectDB (and in JPA) is always at the database object level, i.e. each database object is locked ... to pessimistic locking it is easier to use and more efficient. In the rare cases in which update collision ... object. The initial version of a new entity object (when it is stored in the database for the first time |
81 | Paths and Types in JPQL and Criteria API classes) are represented in JPQL by the following types of expressions: Variables - FROM ... persistable classes can participate in direct comparison using the = and <> operators. But more often they are used in JPQL path expressions that navigate to values of simple types (number, boolean |
80 | Comparison in JPQL and Criteria APIMost JPQL queries use at least one comparison operator in their WHERE clause. Comparison Operators ObjectDB supports two sets of comparison operators, as shown in the following table: Set 1 - JPQL ... Equal To >= >= Equal = == Not Equal <> != The two sets differ in the Equal and the Not Equal operators |
80 | Strings in JPQL and Criteria QueriesString values may appear in JPQL queries in various forms: as string literals - e.g. 'abc', ''. as parameters - when string values are assigned as arguments. as path expressions - in navigation ... '%\%' ESCAPE '\' is evaluated to FALSE. In the expressions above only the first percent character |
78 | Logical Operators in JPQL and Criteria APILogical operators in JPQL and in JPA criteria queries enable composition of complex JPQL boolean ... of logical operators, as shown in the following table: Set 1 - JPQL / SQL Set 2 - Java / JDO AND && OR || NOT ! JPQL follows the SQL notation, while Java uses its own notation (which is also in use by JDOQL |
78 | Numbers in JPQL and Criteria QueriesNumeric values may appear in JPQL queries in many forms: as numeric literals - e.g. 123, -12.5. as parameters - when numeric values are assigned as arguments. as path expressions - in navigation ... ) and the ~ (bitwise complement) operators that are supported in Java and JDO. JPA follows Java |
78 | UPDATE SET Queries in JPA/JPQLExisting entity objects can be updated, as explained in chapter 2, by: Retrieving the entity ... the content of specified entity objects in the database. Updating entity objects in the database using ... with the database. For example, the EntityManager may not be aware that a cached entity object in |
