Field-Level Constraints
Field-level constraints allow you to indicate additional validations that will be applied to fields of a Sheet. These constraints are in addition to the implicit constraints based on types of data. (eg: String, Number) For example, a value is required for every record (RequiredConstraint), or every record must contain a unique value for the field (UniqueConstraint).Required Constraint
Required Constraints indicate that the given field must be provided with a non-null value.A 
null value in this case constitutes an empty cell.Unique Constraint
Unique Constraints indicate that the given field value must only appear once in all the values for that field.null values will appear many times because they are not considered unique as
there is no value to compare.Computed Value
You might notice a ComputedValue type within the Blueprint code. Please do not use this value at this time as it is unsupported and may be deprecated without notice.Sheet-Level
Composite Uniqueness
Composite Uniqueness is a feature where a combination of two or more fields must be unique across an entire Sheet. To implement composite uniqueness, add the following parameters to theconstraints property:
- 
namedefines the name of the constraint
- 
fieldsarray of field keys to consider
- 
typedefines the type of the constraint
- 
strategydefines how to determine uniqueness Can either be:concatconcatenates values from each field defined inside thefieldsarray orhashcreates a sha1 hash using of the values of each field