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Collection Validation

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When defining a Validation Rule, you can use it to validate a collection property. This topic describes collection validation specifics. For general information on the contextual validation concept, refer to the Validation Rules topic.

Collection Property Validation

Built-in validation rules can be applied to a collection property involved in a relationship (marked with the Association attribute). In this instance, a validation rule is evaluated for all the collection elements rather than for the master object, ensuring that each collection element is valid. So, when specifying parameters of a rule applied to a collection property, you need to specify them in the context of a collection element. For instance, the rule's RuleBaseAttribute.TargetCriteria should not contain references to the master object's properties and should only include properties of the collection element. Additionally, you will need to specify a collection element's property that must be checked via the TargetPropertyName named parameter. In the following code snippet, RuleUniqueValue is applied to the Collection property, to ensure that all the collection elements' StringProperty property values are unique:

public class CollectionOwner : BaseObject {

    public CollectionOwner(Session session) : base(session) { }

    [RuleUniqueValue("RuleCollectionValidation", DefaultContexts.Save, 
        TargetPropertyName = "StringProperty")]
    [Association("CollectionOwner-CollectionElements"), Aggregated]
    public XPCollection<CollectionElement> Collection {
        get { return GetCollection<CollectionElement>("Collection"); }

public class CollectionElement : BaseObject {
    private CollectionOwner owner;
    private string stringProperty;

    public CollectionElement(Session session) : base(session) { }

    public string StringProperty {
        get { return stringProperty; }
        set { stringProperty = value; }

    public CollectionOwner Owner {
        get { return owner; }
        set { owner = value; }

Aggregate Functions

When applied to collection properties, certain validation rules, such as the RuleRange and RuleValueComparison rules, can use aggregate functions. The attributes corresponding to these rules expose the TargetCollectionAggregate property that specifies the aggregate function. When a value is assigned to this property (by setting the corresponding named parameter or via the Application Model), the validation rule does not check the collection property's elements. Instead, it checks the specified aggregate function. For example, the following code snippet illustrates the RuleValueComparison rule applied to the Collection property. In this example, the rule ensures that the sum of the collection elements' IntegerProperty property values does not equal zero:

using DevExpress.Data.Filtering;


public class AggregateFunction : BaseObject {

    public AggregateFunction(Session session) : base(session) { }

    [RuleValueComparison("RuleWithAggregateFunction", DefaultContexts.Save,
        ValueComparisonType.NotEquals, 0, TargetPropertyName = "IntegerProperty",
        TargetCollectionAggregate = Aggregate.Sum)]
    [Association("AggregateFunction-AggregateFunctionCollectionElements"), Aggregated]
    public XPCollection<AggregateFunctionCollectionElement> Collection {
        get { return GetCollection<AggregateFunctionCollectionElement>("Collection"); }

public class AggregateFunctionCollectionElement : BaseObject {
    private AggregateFunction owner;
    private int integerProperty;

    public AggregateFunctionCollectionElement(Session session) : base(session) { }

    public int IntegerProperty {
        get { return integerProperty; }
        set { integerProperty = value; }

    public AggregateFunction Owner {
        get { return owner; }
        set { owner = value; }

If the RuleBaseAttribute.TargetCriteria property has been specified, then the demonstrated rule would calculate the sum over the suitable elements only.

The following aggregate functions are available:

Aggregate Function Description
Avg Evaluates the average of the collection elements' property values. Requires the TargetPropertyName to be specified.
Count Evaluates the number of elements contained in the collection. Does not require the TargetPropertyName to be specified.
Exists Evaluates whether a collection element exists, which has a valid TargetPropertyName property's value (the validity is defined by the actual validation rule).
Max Evaluates the maximum of the collection elements' property values. Requires the TargetPropertyName to be specified.
Min Evaluates the minimum of the collection elements' property values. Requires the TargetPropertyName to be specified.
Sum Evaluates the sum of the collection elements' property values. Requires the TargetPropertyName to be specified.

RuleValueComparison is not checked if the collection property is empty. Use the RuleRequiredFieldAttribute instead.

Aggregate Function Values in Custom Message Templates

When customizing validation message templates, you can include the aggregate function value in the template. For this purpose, use the {AggregatedTargetValue} parameter. The following code snippet illustrates this:

using DevExpress.Data.Filtering;


public class MessageTemplate : BaseObject {

    public MessageTemplate(Session session) : base(session) { }

    [RuleRange("RuleWithCustomMessageTemplate", DefaultContexts.Save, 0, 50,
        TargetPropertyName = "DecimalProperty", TargetCollectionAggregate = Aggregate.Sum,
        CustomMessageTemplate = "The sum of the {TargetPropertyName} values must be " +
        "within {MinimumValue} and {MaximumValue} range. The current value is" +
        " {AggregatedTargetValue}")]
    [Association("MessageTemplate-MessageTemplateCollectionElements"), Aggregated]
    public XPCollection<MessageTemplateCollectionElement> Collection {
        get { return GetCollection<MessageTemplateCollectionElement>("Collection"); }

public class MessageTemplateCollectionElement : BaseObject {
    private decimal decimalProperty;
    private MessageTemplate owner;

    public MessageTemplateCollectionElement(Session session) : base(session) { }

    public decimal DecimalProperty {
        get { return decimalProperty; }
        set { decimalProperty = value; }

    public MessageTemplate Owner {
        get { return owner; }
        set { SetPropertyValue("Owner", ref owner, value); }
See Also