136 Queries with JDOQL collection is the entire
Query filter expressions 137 Query filters are expressions that evaluate to a boolean value. They are structured as zero, one, or more boolean expressions separated by logical NOT (complement), AND, and OR operators, in that order of evaluation. Parentheses may be used to alter the default order of evaluation. For readers well versed in formal grammars, the grammar for JDOQL is reproduced in Appendix E, in Backus-Naur Form (BNF). 8.5.1 Supported operators Five logical operators are defined. These are listed and described in Table 8.1. Table 8.1 Logical operators Operator Description ! NOT (complement) Negates the logical expression to its right & Unconditional AND Causes the expressions to its left and right to be evaluated, and returns the result of a logical AND operation of the resulting boolean values && Conditional AND Causes the evaluation of the expression to its left. If this is false, the result of the AND expression is false; otherwise the expression on its right is evaluated, the result of the AND expression being the result of the right-hand boolean expression | Unconditional OR Causes the expressions to its left and right to be evaluated, and returns the result of a logical OR operation of the resulting boolean values | | Conditional OR Causes the evaluation of the expression to its left. If this is true, the result of the OR expression is true; otherwise the expression on its right is evaluated, the result of the OR expression being the result of the right-hand boolean expression JDOQL filters must be non-mutating, which means that their evaluation will have no side effects. Thus there is no justification for using the unconditional logical operators (&, |), and the conditional ones (&&, ||) should be used as a matter of course. Indeed, many JDO implementations replace & with && and | with || during query execution. JDOQL supports a complete set of comparative operators. These return boolean values based on evaluating the results of the left and right-hand expressions. They are shown in Table 8.2.
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