CODEWITHSUNDEEP
grails
kofhearts
kofhearts

Reputation: 3794

When should we add not null constraint when defining a domain?

Many times i find myself in a dilemma when designing a new domain class. When i create a new domain class in Grails i have few properties. I can either add not null constraints on these properties or make them nullable. This choice seems optional in many cases in the domains i create. So, what are some of the good reasons to add not nullable constraints and also not blank constraint. I need few points to understand when should one care about these constraints. Thanks! 

static constraints = {

        title nullable:true, blank:true

    }

Upvotes: 0

Views: 354

Answers (3)

Abhinandan Satpute
Abhinandan Satpute

Reputation: 2678

Scenarios where,

we add constraint :- nullable :false, blank:false

  • property is means of identity
  • property is adding value(importance)
  • property is going to help in reducing query complexity
  • property can not be null or blank just because of business logic.

Upvotes: 1

cfrick
cfrick

Reputation: 37073

nullable means, that the attribute there may be devoid of value. This is also how (SQL) databases model that - so this setting will end up in your table constraints with your (SQL) database (e.g. NOT NULL).

Also (SQL) databases can query for that: is null and is not null. This might lead to some surprising results (e.g. with order).

Being nullable makes e.g. an Boolean tri-state. It can be true, false, or null - so /yes/, /no/, or /no decision made/ (or revoked).

When modelling your DB with GORM a common place for nullable is for 0..1 associations.

Or in short: think of Optional or Maybe.

Upvotes: 1

railsdog
railsdog

Reputation: 1501

You should be thinking about your models... Take a Widget. What attributes are necessary to constitute a Widget? Perhaps it's just a name, or a part number, and all other attributes are nice-to-have's or extra details. Maybe its a name AND part number. Necessary attributes would receive the nullable:false. Any others could be nullable:true.

blank, true or false? Well, I don't see much utility in a blank string as a value. I'd rather deal with a simpler case or null versus not null to indicate if there is data present.

Upvotes: 1

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