Using Caché Objects - InterSystems Documentation

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Class Queries
Class queries provides a tool to look up instances of a class that meet specified criteria. They
allow you to create named SQL statements that are part of a class structure so that applications
can have pre-defined lookups. For example, you can look up instances by some property,
such as by name, or provide a list of instances that meet a particular set of conditions, such
as all the flights from Paris to Madrid.
By creating a class query, you can avoid having to look up a particular object by its internal
ID. Instead, you can create a query that looks based on any class properties that you want.
These can even be specified from user input at runtime.
A class query can be either in SQL or Caché ObjectScript. To create a query, use the Caché
Studio and create one either by hand or using the New Query Wizard.
Class queries are designed for transparent use with the relational aspect of Caché classes. As
stated, they use SQL syntax. When the application invokes the query, it returns values in a
%Library.ResultSet object, which provides robust interface for processing data.
Class queries provide logical comparisons for data values. You can compare whether the
value is greater than, equal to, or less than a certain value and include only the objects with
values that pass the specified test. You can also compare whether the value starts with a certain
string and include these objects in the result set. A query can also perform multiple comparisons.
Because the comparisons support any combination of nested AND and OR operators,
you can require that an object meets one, some, or all of them in order to be added to the
result set.
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