DynamicWhere.ex
DynamicWhere.exv2.1.0·docs

Aggregator

Aggregator is the aggregation function applied inside a GroupBy. Each entry in GroupBy.AggregateBy picks one of the eight functions and a target field — and the result column is named by AggregateBy.Alias.

Values

The two columns at the end tell you whether the function accepts a field at all, and whether that field is constrained to numeric types.

ValueDescriptionSupports Field?Numeric Only?
CountCount items in the group.Optional — when no field, counts all items in the group.No
CountDistinctCount distinct values of the field.RequiredNo
SumationSum of values.RequiredYes
AverageAverage of values.RequiredYes
MinimumMinimum value.RequiredNo (except Boolean)
MaximumMaximum value.RequiredNo (except Boolean)
FirstOrDefaultFirst value in the group.RequiredNo
LastOrDefaultLast value in the group.RequiredNo
Numeric-only constraints
Sumation and Average only accept numeric fields. Minimum and Maximum reject Boolean fields specifically. Violations throw UnsupportedAggregatorForType(agg, type).

Validation rules

RuleError code
Alias must be non-empty and contain no dots.InvalidAlias
Aliases must be unique within an AggregateBy list.AggregationAliasesMustBeUnique
An alias cannot match any GroupBy.Fields entry.AggregationAliasCannotBeGroupByField(alias)
Aggregation field must be a simple type (not complex / navigation).AggregationFieldMustBeSimpleType
Aggregation field cannot be a collection.AggregationFieldCannotBeCollectionType
Sumation / Average on a non-numeric field.UnsupportedAggregatorForType(agg, type)
Minimum / Maximum on a Boolean field.UnsupportedAggregatorForType(agg, type)

JSON example

{
  "fields": ["Category"],
  "aggregateBy": [
    { "field": null,    "alias": "TotalCount",    "aggregator": "Count" },
    { "field": "Id",    "alias": "DistinctIds",   "aggregator": "CountDistinct" },
    { "field": "Price", "alias": "TotalRevenue",  "aggregator": "Sumation" },
    { "field": "Price", "alias": "AvgPrice",      "aggregator": "Average" },
    { "field": "Price", "alias": "MinPrice",      "aggregator": "Minimum" },
    { "field": "Price", "alias": "MaxPrice",      "aggregator": "Maximum" },
    { "field": "Name",  "alias": "FirstName",     "aggregator": "FirstOrDefault" },
    { "field": "Name",  "alias": "LastName",      "aggregator": "LastOrDefault" }
  ]
}

Result (illustrative single group row):

{
  "Category": "Electronics",
  "TotalCount": 15,
  "DistinctIds": 15,
  "TotalRevenue": 5249.85,
  "AvgPrice": 349.99,
  "MinPrice": 9.99,
  "MaxPrice": 1299.99,
  "FirstName": "Adapter Cable",
  "LastName": "Wireless Mouse"
}

C# usage

using DynamicWhere.ex.Enums;

var groupBy = new GroupBy
{
    Fields = new List<string> { "Category" },
    AggregateBy = new List<AggregateBy>
    {
        new AggregateBy { Field = null,    Alias = "TotalCount",   Aggregator = Aggregator.Count },
        new AggregateBy { Field = "Price", Alias = "TotalRevenue", Aggregator = Aggregator.Sumation },
        new AggregateBy { Field = "Price", Alias = "AvgPrice",     Aggregator = Aggregator.Average },
    }
};
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