Aggregation Expressions

Arithmetic Operators

pipeline = [
    {"$project": {
        "total": {"$add": ["$price", "$tax"]},
        "difference": {"$subtract": ["$msrp", "$price"]},
        "tax_amount": {"$multiply": ["$price", 0.1]},
        "unit_price": {"$divide": ["$total", "$quantity"]},
        "remainder": {"$mod": ["$quantity", 12]},
        "absolute": {"$abs": "$discount"},
        "rounded": {"$round": ["$price", 2]}
    }}
]

String Operators

pipeline = [
    {"$project": {
        "full_name": {"$concat": ["$first_name", " ", "$last_name"]},
        "upper_name": {"$toUpper": "$name"},
        "lower_email": {"$toLower": "$email"},
        "name_length": {"$strLenCP": "$name"},
        "initials": {"$substr": ["$name", 0, 1]},
        "domain": {
            "$arrayElemAt": [
                {"$split": ["$email", "@"]},
                1
            ]
        },
        "has_gmail": {
            "$regexMatch": {
                "input": "$email",
                "regex": "@gmail\.com$"
            }
        }
    }}
]

Date Operators

pipeline = [
    {"$project": {
        "year": {"$year": "$created_at"},
        "month": {"$month": "$created_at"},
        "day": {"$dayOfMonth": "$created_at"},
        "day_of_week": {"$dayOfWeek": "$created_at"},
        "hour": {"$hour": "$created_at"},
        "date_string": {
            "$dateToString": {
                "format": "%Y-%m-%d",
                "date": "$created_at"
            }
        },
        "age_days": {
            "$dateDiff": {
                "startDate": "$created_at",
                "endDate": "$$NOW",
                "unit": "day"
            }
        }
    }}
]

Conditional Operators

# $cond - if/then/else
pipeline = [
    {"$project": {
        "status": {
            "$cond": {
                "if": {"$gte": ["$stock", 10]},
                "then": "In Stock",
                "else": "Low Stock"
            }
        }
    }}
]

# $switch - multiple conditions
pipeline = [
    {"$project": {
        "grade": {
            "$switch": {
                "branches": [
                    {"case": {"$gte": ["$score", 90]}, "then": "A"},
                    {"case": {"$gte": ["$score", 80]}, "then": "B"},
                    {"case": {"$gte": ["$score", 70]}, "then": "C"},
                    {"case": {"$gte": ["$score", 60]}, "then": "D"}
                ],
                "default": "F"
            }
        }
    }}
]

# $ifNull - null coalescing
pipeline = [
    {"$project": {
        "name": {"$ifNull": ["$nickname", "$username", "Anonymous"]}
    }}
]

Array Expressions

pipeline = [
    {"$project": {
        "first_tag": {"$arrayElemAt": ["$tags", 0]},
        "last_tag": {"$arrayElemAt": ["$tags", -1]},
        "tag_count": {"$size": "$tags"},
        "has_featured": {"$in": ["featured", "$tags"]},
        "filtered_items": {
            "$filter": {
                "input": "$items",
                "as": "item",
                "cond": {"$gte": ["$$item.price", 10]}
            }
        },
        "item_names": {
            "$map": {
                "input": "$items",
                "as": "item",
                "in": "$$item.name"
            }
        }
    }}
]