Implement MarshalJSON for query results (#114)

calculation/calculation_op.go

@@ -132,32 +132,32 @@ var (
 
 	// For operators that do not require fields.
 	newResultFnsByOpsNoType = map[Op]newResultFn{
-		Count: newCountResult,
+		Count: NewCountResult,
 	}
 
 	// For operators that require fields.
 	newResultFnsByOpsAndType = map[Op]map[field.ValueType]newResultFn{
 		Sum: map[field.ValueType]newResultFn{
-			field.IntType:    newSumResult,
-			field.DoubleType: newSumResult,
-			field.TimeType:   newSumResult,
+			field.IntType:    NewSumResult,
+			field.DoubleType: NewSumResult,
+			field.TimeType:   NewSumResult,
 		},
 		Avg: map[field.ValueType]newResultFn{
-			field.IntType:    newAvgResult,
-			field.DoubleType: newAvgResult,
-			field.TimeType:   newAvgResult,
+			field.IntType:    NewAvgResult,
+			field.DoubleType: NewAvgResult,
+			field.TimeType:   NewAvgResult,
 		},
 		Min: map[field.ValueType]newResultFn{
-			field.IntType:    newMinNumberResult,
-			field.DoubleType: newMinNumberResult,
-			field.StringType: newMinStringResult,
-			field.TimeType:   newMinNumberResult,
+			field.IntType:    NewMinNumberResult,
+			field.DoubleType: NewMinNumberResult,
+			field.StringType: NewMinStringResult,
+			field.TimeType:   NewMinNumberResult,
 		},
 		Max: map[field.ValueType]newResultFn{
-			field.IntType:    newMaxNumberResult,
-			field.DoubleType: newMaxNumberResult,
-			field.StringType: newMaxStringResult,
-			field.TimeType:   newMaxNumberResult,
+			field.IntType:    NewMaxNumberResult,
+			field.DoubleType: NewMaxNumberResult,
+			field.StringType: NewMaxStringResult,
+			field.TimeType:   NewMaxNumberResult,
 		},
 	}
 

calculation/result.go

@@ -1,6 +1,7 @@
 package calculation
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math"
@@ -25,6 +26,9 @@ type Result interface {
 
 	// Value returns the result value.
 	Value() ValueUnion
+
+	// MarshalJSON marshals the result as a JSON object.
+	MarshalJSON() ([]byte, error)
 }
 
 var (
@@ -43,11 +47,12 @@ type countResult struct {
 	v int
 }
 
-func newCountResult() Result {
+// NewCountResult creates a new count result.
+func NewCountResult() Result {
 	return &countResult{}
 }
 
-func (r *countResult) New() Result { return newCountResult() }
+func (r *countResult) New() Result { return NewCountResult() }
 
 func (r *countResult) Add(ValueUnion) { r.v++ }
 
@@ -60,17 +65,18 @@ func (r *countResult) MergeInPlace(other Result) error {
 	return nil
 }
 
-func (r *countResult) Value() ValueUnion { return newNumberUnion(float64(r.v)) }
+func (r *countResult) Value() ValueUnion { return NewNumberUnion(float64(r.v)) }
+
+func (r *countResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
 
 type sumResult struct {
 	v float64
 }
 
-func newSumResult() Result {
-	return &sumResult{}
-}
+// NewSumResult creates a new sum result.
+func NewSumResult() Result { return &sumResult{} }
 
-func (r *sumResult) New() Result { return newSumResult() }
+func (r *sumResult) New() Result { return NewSumResult() }
 
 func (r *sumResult) Add(v ValueUnion) { r.v += v.NumberVal }
 
@@ -83,18 +89,19 @@ func (r *sumResult) MergeInPlace(other Result) error {
 	return nil
 }
 
-func (r *sumResult) Value() ValueUnion { return newNumberUnion(r.v) }
+func (r *sumResult) Value() ValueUnion { return NewNumberUnion(r.v) }
+
+func (r *sumResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
 
 type avgResult struct {
 	s float64
 	c int
 }
 
-func newAvgResult() Result {
-	return &avgResult{}
-}
+// NewAvgResult creates a new average result.
+func NewAvgResult() Result { return &avgResult{} }
 
-func (r *avgResult) New() Result { return newAvgResult() }
+func (r *avgResult) New() Result { return NewAvgResult() }
 
 func (r *avgResult) Add(v ValueUnion) {
 	r.s += v.NumberVal
@@ -111,18 +118,19 @@ func (r *avgResult) MergeInPlace(other Result) error {
 	return nil
 }
 
-func (r *avgResult) Value() ValueUnion { return newNumberUnion(r.s / float64(r.c)) }
+func (r *avgResult) Value() ValueUnion { return NewNumberUnion(r.s / float64(r.c)) }
+
+func (r *avgResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
 
 type minNumberResult struct {
 	hasValues bool
 	v         float64
 }
 
-func newMinNumberResult() Result {
-	return &minNumberResult{}
-}
+// NewMinNumberResult creates a new minimum number result.
+func NewMinNumberResult() Result { return &minNumberResult{} }
 
-func (r *minNumberResult) New() Result { return newMinNumberResult() }
+func (r *minNumberResult) New() Result { return NewMinNumberResult() }
 
 func (r *minNumberResult) Add(v ValueUnion) {
 	if !r.hasValues {
@@ -155,21 +163,22 @@ func (r *minNumberResult) MergeInPlace(other Result) error {
 
 func (r *minNumberResult) Value() ValueUnion {
 	if !r.hasValues {
-		return newNumberUnion(nan)
+		return NewNumberUnion(nan)
 	}
-	return newNumberUnion(r.v)
+	return NewNumberUnion(r.v)
 }
 
+func (r *minNumberResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
+
 type minStringResult struct {
 	hasValues bool
 	v         string
 }
 
-func newMinStringResult() Result {
-	return &minStringResult{}
-}
+// NewMinStringResult creates a new minimum string result.
+func NewMinStringResult() Result { return &minStringResult{} }
 
-func (r *minStringResult) New() Result { return newMinStringResult() }
+func (r *minStringResult) New() Result { return NewMinStringResult() }
 
 func (r *minStringResult) Add(v ValueUnion) {
 	if !r.hasValues {
@@ -202,21 +211,22 @@ func (r *minStringResult) MergeInPlace(other Result) error {
 
 func (r *minStringResult) Value() ValueUnion {
 	if !r.hasValues {
-		return newStringUnion(emptyString)
+		return NewStringUnion(emptyString)
 	}
-	return newStringUnion(r.v)
+	return NewStringUnion(r.v)
 }
 
+func (r *minStringResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
+
 type maxNumberResult struct {
 	hasValues bool
 	v         float64
 }
 
-func newMaxNumberResult() Result {
-	return &maxNumberResult{}
-}
+// NewMaxNumberResult creates a new maximum number result.
+func NewMaxNumberResult() Result { return &maxNumberResult{} }
 
-func (r *maxNumberResult) New() Result { return newMaxNumberResult() }
+func (r *maxNumberResult) New() Result { return NewMaxNumberResult() }
 
 func (r *maxNumberResult) Add(v ValueUnion) {
 	if !r.hasValues {
@@ -249,21 +259,22 @@ func (r *maxNumberResult) MergeInPlace(other Result) error {
 
 func (r *maxNumberResult) Value() ValueUnion {
 	if !r.hasValues {
-		return newNumberUnion(nan)
+		return NewNumberUnion(nan)
 	}
-	return newNumberUnion(r.v)
+	return NewNumberUnion(r.v)
 }
 
+func (r *maxNumberResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
+
 type maxStringResult struct {
 	hasValues bool
 	v         string
 }
 
-func newMaxStringResult() Result {
-	return &maxStringResult{}
-}
+// NewMaxStringResult creates a new maximum string result.
+func NewMaxStringResult() Result { return &maxStringResult{} }
 
-func (r *maxStringResult) New() Result { return newMaxStringResult() }
+func (r *maxStringResult) New() Result { return NewMaxStringResult() }
 
 func (r *maxStringResult) Add(v ValueUnion) {
 	if !r.hasValues {
@@ -296,11 +307,13 @@ func (r *maxStringResult) MergeInPlace(other Result) error {
 
 func (r *maxStringResult) Value() ValueUnion {
 	if !r.hasValues {
-		return newStringUnion(emptyString)
+		return NewStringUnion(emptyString)
 	}
-	return newStringUnion(r.v)
+	return NewStringUnion(r.v)
 }
 
+func (r *maxStringResult) MarshalJSON() ([]byte, error) { return json.Marshal(r.Value()) }
+
 // ResultArray is an array of calculation result.
 type ResultArray []Result
 

calculation/value.go

@@ -1,7 +1,9 @@
 package calculation
 
 import (
+	"encoding/json"
 	"fmt"
+	"math"
 
 	"github.com/xichen2020/eventdb/document/field"
 	"github.com/xichen2020/eventdb/x/compare"
@@ -16,18 +18,40 @@ const (
 	StringType
 )
 
+var (
+	nullBytes = []byte("null")
+)
+
 // ValueUnion is a value union.
 type ValueUnion struct {
 	Type      ValueType
 	NumberVal float64
 	StringVal string
 }
 
-func newNumberUnion(v float64) ValueUnion {
+// MarshalJSON marshals value as a JSON object.
+func (u ValueUnion) MarshalJSON() ([]byte, error) {
+	switch u.Type {
+	case NumberType:
+		// NaN cannot be marshalled as JSON, so marshal it as null.
+		if math.IsNaN(u.NumberVal) {
+			return nullBytes, nil
+		}
+		return json.Marshal(u.NumberVal)
+	case StringType:
+		return json.Marshal(u.StringVal)
+	default:
+		return nil, fmt.Errorf("unexpected value type %v", u.Type)
+	}
+}
+
+// NewNumberUnion creates a new number union.
+func NewNumberUnion(v float64) ValueUnion {
 	return ValueUnion{Type: NumberType, NumberVal: v}
 }
 
-func newStringUnion(v string) ValueUnion {
+// NewStringUnion creates a new string union.
+func NewStringUnion(v string) ValueUnion {
 	return ValueUnion{Type: StringType, StringVal: v}
 }
 
@@ -100,31 +124,31 @@ func AsValueFns(fieldTypes field.OptionalTypeArray) ([]FieldValueToValueFn, erro
 }
 
 func nullToValue(v *field.ValueUnion) ValueUnion {
-	return newNumberUnion(0)
+	return NewNumberUnion(0)
 }
 
 func boolToValue(v *field.ValueUnion) ValueUnion {
 	var val float64
 	if v.BoolVal {
 		val = 1
 	}
-	return newNumberUnion(val)
+	return NewNumberUnion(val)
 }
 
 func intToValue(v *field.ValueUnion) ValueUnion {
-	return newNumberUnion(float64(v.IntVal))
+	return NewNumberUnion(float64(v.IntVal))
 }
 
 func doubleToValue(v *field.ValueUnion) ValueUnion {
-	return newNumberUnion(v.DoubleVal)
+	return NewNumberUnion(v.DoubleVal)
 }
 
 func stringToValue(v *field.ValueUnion) ValueUnion {
-	return newStringUnion(v.StringVal)
+	return NewStringUnion(v.StringVal)
 }
 
 func timeToValue(v *field.ValueUnion) ValueUnion {
-	return newNumberUnion(float64(v.TimeNanosVal))
+	return NewNumberUnion(float64(v.TimeNanosVal))
 }
 
 var (

document/field/value.go

@@ -1,6 +1,7 @@
 package field
 
 import (
+	"encoding/json"
 	"fmt"
 	"math"
 
@@ -27,6 +28,8 @@ const (
 var (
 	// NumValidFieldTypes returns the number of valid field types.
 	NumValidFieldTypes = len(validTypes)
+
+	nullBytes = []byte("null")
 )
 
 // IsValid returns true if this is a valid value type.
@@ -197,6 +200,26 @@ func NewTimeUnion(v int64) ValueUnion {
 	}
 }
 
+// MarshalJSON marshals value as a JSON object.
+func (v ValueUnion) MarshalJSON() ([]byte, error) {
+	switch v.Type {
+	case NullType:
+		return nullBytes, nil
+	case BoolType:
+		return json.Marshal(v.BoolVal)
+	case IntType:
+		return json.Marshal(v.IntVal)
+	case DoubleType:
+		return json.Marshal(v.DoubleVal)
+	case StringType:
+		return json.Marshal(v.StringVal)
+	case TimeType:
+		return json.Marshal(v.TimeNanosVal)
+	default:
+		return nil, fmt.Errorf("unknown value type: %v", v.Type)
+	}
+}
+
 // Equal returns true if two value unions are considered equal.
 func (v *ValueUnion) Equal(other *ValueUnion) bool {
 	if v == nil && other == nil {