100 lines
3.7 KiB
Markdown
100 lines
3.7 KiB
Markdown
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---
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title: 'Searches'
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weight: 80
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---
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## Searches
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As is custom for every framework, querying, or searching, the model must be
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possible. Strolch searches are implemented using the `StrolchSearch` class and
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one of its concrete implementations: `ResourceSearch`, `OrderSearch`,
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`ActivitySearch`.
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A Strolch element always has two identifiers: `Type` and `Id`. The type is
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important as it classifies an element. So if a car and a house would be modelled
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in Strolch, then those would both be a `Resource`, but one of type `Car`
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and the other of type `House`. Both would have different parameters. Thus when
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searching for objects, the first thing to do is define the type of object being
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searched.
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The Strolch search API is very expressive and offers multiple ways to perform
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the same search. The search API consists of three components: The search
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classes, the search expressions and the search predicates. The concept was taken
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from the [Apache Camel](https://camel.apache.org/) project.
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There are four main search classes:
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* RootElementSearch - search for any of Resource, Order or Activity elements
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* ResourceSearch - search for Resources
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* OrderSearch - search for Orders
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* ActivitySearch - search for Activities
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No search is useful without a `where` clause, which are called search
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expressions. When writing a search, there are multiple ways to add such where
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clauses. Either
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* override the `define()`-method in your sub class and add the where clauses by
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calling the `where()` method, or
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* define special methods on the class e.g. `byColor()` which also calls the
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`where()`-method to add a search expression, or
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* directly call the `where()`-method after instantiating a search.
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When extending the class, then the search expressions are available as methods
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on the super class, otherwise you can statically import them from
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[ExpressionsSupport](https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/main/java/li/strolch/search/ExpressionsSupport.java)
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.
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And of course a where clause needs operators, which are called search
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predicates. Just as search expressions are available in sub classes, so are
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search predicates and can also be statically imported through
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[PredicatesSupport](https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/main/java/li/strolch/search/PredicatesSupport.java)
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.
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Examples of search expressions with search predicates follow:
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```java
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ResourceSearch search=new ResourceSearch();
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// predicate either as parameter, or chained
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search.where(id().isEqualTo("myId"));
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search.where(id(isEqualTo("myId")));
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// negating
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search.where(id(isEqualTo("myId")).not());
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search.where(param("bagId","paramId").isIn(Arrays.asList("red","blue","green")));
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search.where(paramNull("bagId","paramId")));
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// boolean operations
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search.where(id(isEqualTo("myId")) //
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.or(name(isEqualTo("myName"))));
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```
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Note how the predicates can be chained to the search expression, or passed as a
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parameter to the expression.
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In addition to using predefined search search expressions, one can also just
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pass a lambda expression which performs a custom filter:
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```java
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personSearch.where(person -> person.getName().length() == 3);
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```
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See
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the [StrolchSearchTest](https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/test/java/li/strolch/search/StrolchSearchTest.java)
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for many ways in which you can implement tests.
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{{% notice tip %}} Note that strolch searches requires privileges, thus when you
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use a strolch search, add it to the role of the user in `PrivilegeRoles.xml`:
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{{% /notice %}}
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```xml
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<Privilege name="li.strolch.search.StrolchSearch" policy="DefaultPrivilege">
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<Allow>internal
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</Allow> <!-- internal used for when the search is done in an internal service -->
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<Allow>li.strolch.bookshop.search.BookSearch</Allow>
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</Privilege>
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```
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