//existing 
var conditionalExpression = new Expression
{
    ExpressionStatement = "#price = :price",
    ExpressionAttributeNames = { ["#price"] = "Price" },
    ExpressionAttributeValues = { [":price"] = 50 }
};

//build 
var expression = ConditionExpressionBuilder.New().WithName("Price").Equal(50).Build();

//existing 
var conditionalExpression = new Expression
                    {
                        ExpressionStatement = "attribute_not_exists(#id) AND #price <> :price",
                        ExpressionAttributeNames = { ["#id"] = "Id", ["#price"] = "Price" },
                        ExpressionAttributeValues = { [":price"] = 500 }
                    };

//build 
var expression = ConditionExpressionBuilder.New().WithName("Id").AttributeExists().
                And(ConditionExpressionBuilder.New().WithName("Price").Equal(50)).Build();

//existing 
var updateExpression = new Expression
{
    ExpressionStatement = "SET #garbage = :garbage",
    ExpressionAttributeNames = { ["#garbage"] = "Garbage" },
    ExpressionAttributeValues = { [":garbage"] = "asdf" }
};

//build 
var expression = UpdateExpressionBuilder.New().
    Set(NameBuilder.New("Garbage"), SetValueBuilder.New().WithValue("asdf")).Build();

//existing 
var updateExpression = new Expression
{
    ExpressionStatement = "SET #price = #price + :inc",
    ExpressionAttributeNames = { ["#price"] = "Price" },
    ExpressionAttributeValues = { [":inc"] = 1 }
}

//build 
var expression = UpdateExpressionBuilder.New().
    Set(NameBuilder.New("Price"), SetValueBuilder.New().WithName("Price").Plus(1))
    .Build();