Reference

Reference

Both overloads are in Vali_Flow.NoSql.DynamoDB.Extensions.ValiFlowDynamoExtensions.

ToDynamoDB<T>(this ValiFlow<T> flow, Func<object?, AttributeValue?>? customConverter = null)

Translates the conditions accumulated in a ValiFlow<T> builder into a DynamoFilterExpression.

Parameter	Type	Required	Description
flow	ValiFlow<T>	Yes	The builder containing the conditions.
customConverter	Func<object?, AttributeValue?>?	No	Hook for mapping CLR types not handled by the built-in switch. Return null to fall through to the default conversion.

Returns: DynamoFilterExpression — apply to ScanRequest or QueryRequest.

ToDynamoDB<T>(this Expression<Func<T, bool>> expression, Func<object?, AttributeValue?>? customConverter = null)

Same translation for a pre-built Expression<Func<T, bool>>.

Expression<Func<User, bool>> expr = u => u.IsActive && u.Age >= 21;
DynamoFilterExpression f = expr.ToDynamoDB();

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DynamoFilterExpression

DynamoFilterExpression is a sealed class that encapsulates the three values DynamoDB needs:

Property	Type	Description
FilterExpression	string	The expression string, e.g. "(#f0 = :v0 AND #f1 > :v1)".
ExpressionAttributeNames	IReadOnlyDictionary<string, string>	Maps placeholders (#f0, #f1, …) to actual attribute names.
ExpressionAttributeValues	IReadOnlyDictionary<string, AttributeValue>	Maps placeholders (:v0, :v1, …) to AttributeValue instances.

The translator generates sequential placeholders (#f0, #f1, … for names; :v0, :v1, … for values) to avoid collisions and to sidestep DynamoDB reserved word conflicts.

IReadOnlyDictionary<K,V> does not implement IDictionary<K,V> directly. Call .ToDictionary() when the SDK requires Dictionary<string, string> or Dictionary<string, AttributeValue>.

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Supported Operations

ValiFlow method	IR node	DynamoDB FilterExpression
.EqualTo(x => x.Field, v)	EqualNode(IsNegated: false)	#f0 = :v0
.NotEqualTo(x => x.Field, v)	EqualNode(IsNegated: true)	#f0 <> :v0
.GreaterThan(x => x.Field, v)	ComparisonNode(GT)	#f0 > :v0
.GreaterThanOrEqualTo(x => x.Field, v)	ComparisonNode(GTE)	#f0 >= :v0
.LessThan(x => x.Field, v)	ComparisonNode(LT)	#f0 < :v0
.LessThanOrEqualTo(x => x.Field, v)	ComparisonNode(LTE)	#f0 <= :v0
.Contains(x => x.Field, "txt")	LikeNode(Contains)	contains(#f0, :v0)
.StartsWith(x => x.Field, "pre")	LikeNode(StartsWith)	begins_with(#f0, :v0)
.EndsWith(x => x.Field, "suf")	LikeNode(EndsWith)	throws NotSupportedException
.In(x => x.Field, list)	InNode	#f0 IN (:v0, :v1, …)
.IsNull(x => x.Field)	NullNode(IsNull)	attribute_not_exists(#f0)
.IsNotNull(x => x.Field)	NullNode(IsNotNull)	attribute_exists(#f0)
.And(a, b)	AndNode	(a AND b)
.Or(a, b)	OrNode	(a OR b)
.Not(inner)	NotNode	NOT (inner)

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Type Mapping

The built-in ToAttributeValue switch handles these CLR types:

CLR type	AttributeValue produced
null	{ NULL = true }
bool	{ BOOL = b }
string	{ S = s }
int	{ N = "value" }
long	{ N = "value" }
double	{ N = "value" } (InvariantCulture)
float	{ N = "value" } (InvariantCulture)
decimal	{ N = "value" } (InvariantCulture)
Guid	{ S = g.ToString() }
Enum	{ N = "underlying_int64" }
anything else	{ S = v.ToString() }

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Custom Value Converter

Use customConverter when your domain types are not in the table above or when you need different AttributeValue representation than the default.

The converter is called before the built-in switch. Return null to let the default handle the value.

// Domain type
record Money(decimal Amount, string Currency);

// Converter: store Money as a number (amount only)
DynamoFilterExpression f = new ValiFlow<Order>()
    .GreaterThan(x => x.Total, new Money(500m, "USD"))
    .ToDynamoDB(value =>
    {
        if (value is Money m)
            return new AttributeValue { N = m.Amount.ToString(CultureInfo.InvariantCulture) };
        return null;
    });

Storing a DateTimeOffset as an ISO-8601 string in DynamoDB:

DynamoFilterExpression f = new ValiFlow<Event>()
    .GreaterThan(x => x.StartsAt, DateTimeOffset.UtcNow)
    .ToDynamoDB(value =>
    {
        if (value is DateTimeOffset dto)
            return new AttributeValue { S = dto.ToString("O") };
        return null;
    });

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Advanced Example

var filter = new ValiFlow<Order>()
    .GreaterThan(o => o.Total, 500m)
    .EqualTo(o => o.Status, "Pending")
    .ToDynamoDB();