You can use .Value in an OCL expression when you need a non-null numeric result from a nullable numeric value.

What .Value returns

.Value returns the underlying value of a nullable number. If the value has not been assigned, it returns 0.

Use it where an expression requires a number but the source attribute or calculated result may be null. This prevents a nullable numeric value from causing a null result when you need a numeric value for a calculation.

For example, if Price is nullable:

product.Price.Value

• When product.Price is 25, the expression returns 25.
• When product.Price has no assigned value, the expression returns 0.

Supported types

.Value is available for nullable numeric types.

Type	Result when the value is null
Integer	0
Decimal	0
Double	0
Int64	0

Use .Value in totals

Apply .Value to the result of an aggregate when the total itself must be non-null.

For example, calculate the total price of all products:

Product.allinstances.Price->sum.Value

This returns the summed price when a value is available and returns 0 when the result has no underlying value.

You can instead convert each product price before calculating the sum:

Product.allinstances->collect(i | i.Price.Value)->sum

In this expression, each product with an unassigned Price contributes 0 to the collection before sum is evaluated.

Choose where to apply it

Requirement	Expression pattern	Example
You need a non-null value from one nullable numeric attribute.	Apply .Value to the attribute.	product.Price.Value
You need a non-null aggregate result.	Apply .Value after the aggregate.	Product.allinstances.Price->sum.Value
Each nullable value must become 0 before an aggregate calculation.	Apply .Value inside collect.	i.Price.Value)->sum

Check for null instead when null has meaning

Use .Value only when treating an unassigned number as 0 is correct for the rule. For example, an unassigned price and a price explicitly set to zero produce the same result after .Value.

If your rule must distinguish those cases, test the value with isNull or notNull before using it.

See also

• Documentation:OCLOperators isNull
• Documentation:OCLOperators notNull
• Documentation:OCLOperators minValue
• Documentation:OCLOperators maxValue