REST 查询语言 - 实现 OR 操作
1、概览
本文将扩展 上一篇文章 中实现的高级搜索操作，在 REST API 查询语言中加入基于 OR 的搜索条件。
2、实现方法
以前，search 查询参数中的所有条件都是由 AND 运算符组成的条件。
现在，使用标志来指示必须使用 OR 运算符组合条件。
http://localhost:8080/users?search=firstName:john,'lastName:doe
注意，这里用单引号标记了条件 lastName，以示区别。我们会在条件值对象 SpecSearchCriteria 中捕获 OR 运算符的 Predicate：
public SpecSearchCriteria(
String orPredicate, String key, SearchOperation operation, Object value) {
super();
this.orPredicate
= orPredicate != null
&& orPredicate.equals(SearchOperation.OR_PREDICATE_FLAG);
this.key = key;
this.operation = operation;
this.value = value;
}
3、改进 UserSpecificationBuilder
修改 UserSpecificationBuilder，以在构建 Specification<User> 时考虑 OR 条件：
public Specification<User> build() {
if (params.size() == 0) {
return null;
}
Specification<User> result = new UserSpecification(params.get(0));
for (int i = 1; i < params.size(); i++) {
result = params.get(i).isOrPredicate()
? Specification.where(result).or(new UserSpecification(params.get(i)))
: Specification.where(result).and(new UserSpecification(params.get(i)));
}
return result;
}
4、改进 UserController
最后，在 Controller 中设置一个新的 REST 端点，以使用带 OR 运算符的搜索功能。
改进后的解析逻辑会提取特殊标记，帮助识别带有 OR 运算符的条件：
@GetMapping("/users/espec")
@ResponseBody
public List<User> findAllByOrPredicate(@RequestParam String search) {
Specification<User> spec = resolveSpecification(search);
return dao.findAll(spec);
}
protected Specification<User> resolveSpecification(String searchParameters) {
UserSpecificationsBuilder builder = new UserSpecificationsBuilder();
String operationSetExper = Joiner.on("|")
.join(SearchOperation.SIMPLE_OPERATION_SET);
Pattern pattern = Pattern.compile(
"(\\p{Punct}?)(\\w+?)("
+ operationSetExper
+ ")(\\p{Punct}?)(\\w+?)(\\p{Punct}?),");
Matcher matcher = pattern.matcher(searchParameters + ",");
while (matcher.find()) {
builder.with(matcher.group(1), matcher.group(2), matcher.group(3),
matcher.group(5), matcher.group(4), matcher.group(6));
}
return builder.build();
}
5、Web 端点测试
测试新端点，按 firstName 等于 john 或者 lastName 等于 doe 来检索用户。注意，参数 lastName 带有单引号，这使它成为一个 OR Predicate。
private String EURL_PREFIX
= "http://localhost:8082/spring-rest-full/auth/users/espec?search=";
@Test
public void givenFirstOrLastName_whenGettingListOfUsers_thenCorrect() {
Response response = givenAuth().get(EURL_PREFIX + "firstName:john,'lastName:doe");
String result = response.body().asString();
assertTrue(result.contains(userJohn.getEmail()));
assertTrue(result.contains(userTom.getEmail()));
}
6、持久层测试
在持久层检索 firstName 等于 john 或 lastName 等于 doe 的记录（同上）：
@Test
public void givenFirstOrLastName_whenGettingListOfUsers_thenCorrect() {
UserSpecificationsBuilder builder = new UserSpecificationsBuilder();
SpecSearchCriteria spec
= new SpecSearchCriteria("firstName", SearchOperation.EQUALITY, "john");
SpecSearchCriteria spec1
= new SpecSearchCriteria("'","lastName", SearchOperation.EQUALITY, "doe");
List<User> results = repository
.findAll(builder.with(spec).with(spec1).build());
assertThat(results, hasSize(2));
assertThat(userJohn, isIn(results));
assertThat(userTom, isIn(results));
}
7、替代方法
在另一种方法中，可以提供更像 SQL 查询的完整 WHERE 子句的搜索查询。
例如，按 firstName 和 age 进行更复杂的搜索：
http://localhost:8080/users?search=( firstName:john OR firstName:tom ) AND age>22
注意，用空格分隔了各个条件、运算符和分组括号，以形成一个有效的中缀表达式（infix expression）。
用 CriteriaParser 来解析中缀表达式。CriteriaParser 会将给定的中缀表达式拆分为标记（条件、括号、AND & OR 操作符），并为其创建一个后缀表达式：
public Deque<?> parse(String searchParam) {
Deque<Object> output = new LinkedList<>();
Deque<String> stack = new LinkedList<>();
Arrays.stream(searchParam.split("\\s+")).forEach(token -> {
if (ops.containsKey(token)) {
while (!stack.isEmpty() && isHigerPrecedenceOperator(token, stack.peek())) {
output.push(stack.pop().equalsIgnoreCase(SearchOperation.OR_OPERATOR)
? SearchOperation.OR_OPERATOR : SearchOperation.AND_OPERATOR);
}
stack.push(token.equalsIgnoreCase(SearchOperation.OR_OPERATOR)
? SearchOperation.OR_OPERATOR : SearchOperation.AND_OPERATOR);
} else if (token.equals(SearchOperation.LEFT_PARANTHESIS)) {
stack.push(SearchOperation.LEFT_PARANTHESIS);
} else if (token.equals(SearchOperation.RIGHT_PARANTHESIS)) {
while (!stack.peek().equals(SearchOperation.LEFT_PARANTHESIS)) {
output.push(stack.pop());
}
stack.pop();
} else {
Matcher matcher = SpecCriteraRegex.matcher(token);
while (matcher.find()) {
output.push(new SpecSearchCriteria(
matcher.group(1),
matcher.group(2),
matcher.group(3),
matcher.group(4),
matcher.group(5)));
}
}
});
while (!stack.isEmpty()) {
output.push(stack.pop());
}
return output;
}
在 GenericSpecificationBuilder 中添加一个新方法，从后缀表达式中构建搜索 Specification：
public Specification<U> build(Deque<?> postFixedExprStack,
Function<SpecSearchCriteria, Specification<U>> converter) {
Deque<Specification<U>> specStack = new LinkedList<>();
while (!postFixedExprStack.isEmpty()) {
Object mayBeOperand = postFixedExprStack.pollLast();
if (!(mayBeOperand instanceof String)) {
specStack.push(converter.apply((SpecSearchCriteria) mayBeOperand));
} else {
Specification<U> operand1 = specStack.pop();
Specification<U> operand2 = specStack.pop();
if (mayBeOperand.equals(SearchOperation.AND_OPERATOR)) {
specStack.push(Specification.where(operand1)
.and(operand2));
}
else if (mayBeOperand.equals(SearchOperation.OR_OPERATOR)) {
specStack.push(Specification.where(operand1)
.or(operand2));
}
}
}
return specStack.pop();
最后，在 UserController 中添加另一个 REST 端点，使用新的 CriteriaParser 解析复杂表达式：
@GetMapping("/users/spec/adv")
@ResponseBody
public List<User> findAllByAdvPredicate(@RequestParam String search) {
Specification<User> spec = resolveSpecificationFromInfixExpr(search);
return dao.findAll(spec);
}
protected Specification<User> resolveSpecificationFromInfixExpr(String searchParameters) {
CriteriaParser parser = new CriteriaParser();
GenericSpecificationsBuilder<User> specBuilder = new GenericSpecificationsBuilder<>();
return specBuilder.build(parser.parse(searchParameters), UserSpecification::new);
}
8、总结
本文改进了 REST 查询语言，使其能够使用 OR 运算符进行搜索。
Ref：https://www.baeldung.com/rest-api-query-search-or-operation
