Article
YURI MARX GOMES · Mar 1, 2021 3m read

Day 4: Developing with InterSystems Objects and SQL

I'm participating in the Developing with InterSystems Objects and SQL with Joel Solon. The course is very nice and I will share with you some tips I got during the training. Tips presented in the day 4:

  1. All data are stored in Globals and Global names start with ^. Example of global: ^animal. Global can have multiples locations to the data ("sub data"). Example: ^animal(1).
  2. ^%* globals are accessible from any system-wide (from any namespace).
  3. Globals enables IRIS to support multimodel data (object, relational, document, multidimensional, etc).
  4. To see globals go the Management Portal > Explorer > Globals > Select Global > View or in Terminal type do ^%G or zwrite ^global.
  5. There are an automatic correspondence between persistent classes and SQL Tables:
    1. Package is SQL Schema;
    2. Class is a Table;
    3. Property is a Column;
    4. Method is a Store Procedure; (when sqlProc);
    5. Relationship between classes is a SQL Foreign Key constraint (must be bi-directional);
    6. Object is a Row.
  6. One table can correspond to multiple classes, but serial class is part of the table of the persistent class (don't have a specific table).
  7. One class can correspond to multiple tables.
  8. We have some classes types:
    1. Non-registered: not class object (container for methods only);
    2. Registered: transient objects;
    3. Persistent: SQL persistence in tables;
    4. Serial: SQL persistence in the main table (serial is embedded);
    5. Datatype: not class object is used to do new validations and conversions to base data types.
  9. Classes can be composed by:
    1. Properties;
    2. Methods;
    3. Class queries: SQL Select statements;
    4. Parameters: user constants or system constants to configure the class behavior;
    5. Foreign keys: to referencial integrity;
    6. Indexes: to improve performance and do unique values;
    7. Triggers: fire methods associated with persistence events;
    8. XData: XML or JSON definitions associated with the class;
    9. Storage: description of the data storage.
  10. Classes by convention has first letter of the word in Capital. Example: CountryOrigin. Parameters are all capital. Example: COLORNUMBER.
  11. Class attributes qualify/configure a class. Example [SqlTableName = Animal] set the table name to a class. [Final] not allows inheritence. [Private] not allows call methods or use properties for non-subclasses.
  12. Internally IRIS generate Get and Set to properties, and are not visible but can be declared to change the behavior.
  13. Is possible override a method of the superclass, to do this, repeat the class name, the arguments. Is possible increase the number of arguments, not decrease.
  14. Use ##super() to call base class method.
  15. To create abstract class use [Abstract] and prevent instantiation.
  16. Is possible extends multiple classes. Example Class Person extends (%Persistent, %Animal). (Persistent must be the fisrt in the extends, see joel tip in the comments)
  17. REST is REpresentational State Transfer. Is based in the HTTP protocol. Use HTTP verbs: GET (select), POST (insert), PUT (update) and DELETE (delete). 
  18. For expose your class as REST resource extend from %CSP.REST.
  19. Use URLMap inside XData block to configure the routes of your REST service. Using the Portal, create a Web Application, enable REST and specify Dispatch class.
  20. %JSONAdaptor provides convertion between objects and JSON. Use obj.%JSONImport(jsonObj) to assign DynamicObject to a object. Use obj.%JSONExportToString(.jsonString) to write a JSON String to a object.
  21. %JSON.Formatter format a JSON String for human readability.
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Replies

Good tips! Congrats!

Could you give an example for items 6 and 7?

I always thought that the relationship was a class for a table.

6 & 7 are side effects of object inheritance.
Think of a class Person.
But Employee Extends Person
Similar Students Extends Person too
So you have 3 tables but all are Persons  Some with extension some not.  

@6: Table Employee corresponds to class Person and to class Employee

@7: So class person corresponds to Table PERSON, EMPLOYEE , STUDENT

Regarding 9, can we change the stored information manually? I know it is generated automatically.

@9.9.  storage is generated once if not existing yet.
you may change it manually (typically data location global) as long as there is nothing stored yet
otherwise you lose the existing content. Or you copy it to the new location.
My article The adopted Bitmap shows such an example [actually also in contest}

If there is no storage definition then a storage definition whose type is %Storage.Persistent is created when compiling the class. This is done before the storage definition is compiled (every class member is compiled by the class compiler). Then, when the storage definition is compiled and if the type is %Storage.Persistent then the %Storage.Persistent.STORAGECOMPILERCLASS will generate a full storage definition for the current class definition.

What does that mean? Well - if this is the first time this storage definition has been compiled then it is most likely empty, other than the type class. The STORAGECOMPILERCLASS will generate a complete storage definition. But even if the storage definition is already defined, the STORAGECOMPILERCLASS still reviews that definition. If there are any changes detected to the class definition then the storage definition is updated to reflect those changes.

That means that the user can manually edit the storage definition at any time and the storage compiler will simply make sure that the definition is "complete" - no missing properties, no missing indexes, and so on.

Bottom line is that the user is free to make any desired changes, including deleting the storage definition completely.

Keep in mind that some changes can make the compiled class incompatible with existing data.

Hello YURI MARX GOMES,

Thank you for your articles.

Always good tips

Point 5-5: Relationship on the object side is bi-directional. Class A has a reference to class B, and class B has a collection of references to class A. On the SQL side, table A has a reference to table B, along with automatic referential integrity.

Point 16: Important: for a class to be persistent, %Persistent must be the first class. So the example should be: Class Person extends (%Persistent, Animal)

Just to clarify - inheritance considers the primary super class hierarchy. %Persistent must be the first class some where in the primary super class hierarchy. Sample.Employee extends Sample.Person which extends %Library.Persistent.