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Path expressions usage examples

This page contains advanced examples of using path expressions to select elements from a document modeled in Aerospike as nested map and list structures.

The quickstart guide covers a common use case: filtering and selecting products and their in-stock variants. This section highlights advanced capabilities unlocked by path expressions.

Accessing iteration data from a map key, list index or element value with a LoopVar

When using a path expression to iterate over map or lsit elements, you can assign data from the element in this iteration to loop variables.

Example: Select only products whose key starts with SKU 1000.

Exp filterOnKey = Exp.regexCompare("10000.*", RegexFlag.NONE, Exp.stringLoopVar(LoopVarPart.MAP_KEY));


// Operation
Record record = client.operate(null, key,
    CdtOperation.selectByPath("catalog", Exp.SELECT_MATCHING_TREE,
        CTX.allChildren(),
        CTX.allChildrenWithFilter(filterOnKey)));


System.out.println(record.getMap("catalog"));

Expected output:

 {
  "inventory": {
    "10000001": { ... },
    "10000002": { ... }
  }
}

✅ Only products whose keys start with 1000 are included.

Use alternative return modes with SelectFlags

Sometimes you don’t want the full tree, but just the map keys or values.

Example: Return only the SKUs of in-stock variants for featured products that follow a map/dictionary structure.

// Operation
Record readResult = client.operate(null, key,
    CdtOperation.selectByPath("catalog", Exp.SELECT_MAP_KEY | Exp.SELECT_NO_FAIL,
        CTX.allChildren(),
        CTX.allChildrenWithFilter(filterOnFeatured),
        CTX.mapKey(Value.get("variants")),
        CTX.allChildrenWithFilter(filterOnVariantInventory)
    )
);


System.out.println(readResult.getList("catalog"));

Expected output:

["2001","2003"]

✅ Only the keys from SKU 10000001, Classic T-Shirt are returned.

⚠️ Item 50000009, Smart TV, has list-backed variants, so there are no map keys to return.

Modify nested elements with modifyByPath

You can update selected values in place.

Example: Increase quantity by 10 for all in-stock variants of featured products.

// Increment quantity by 10 and return the modified map
Expression incrementQuantity = Exp.build(
    MapExp.put(
        MapPolicy.Default,
        Exp.val("quantity"),  // key to update
        Exp.add(              // new value: current quantity + 10
            MapExp.getByKey(MapReturnType.VALUE, Exp.Type.INT,
                Exp.val("quantity"),
                Exp.mapLoopVar(LoopVarPart.VALUE)),
            Exp.val(10)
        ),
        Exp.mapLoopVar(LoopVarPart.VALUE)  // map to update
    )
);


client.operate(null, key,
    CdtOperation.modifyByPath("catalog", Exp.MODIFY_DEFAULT, incrementQuantity,
        CTX.allChildren(),
        CTX.allChildrenWithFilter(filterOnFeatured),
        CTX.mapKey(Value.get("variants")),
        CTX.allChildrenWithFilter(filterOnVariantInventory)
    )
);


Record readResult = client.get(null, key);


System.out.println(readResult.getList("catalog"));

Expected Record Modification (diff excerpt):

{
  "inventory": {
    "10000001": {
      "category": "clothing",
      "featured": true,
      "name": "Classic T-Shirt",
      "description": "A lightweight cotton T-shirt perfect for everyday wear.",
      "variants": {
        "2001": { "size": "S", "price": 25, "quantity": 110 }, // 100 -> 110
        "2003": { "size": "L", "price": 27, "quantity": 60 } // 50 -> 60
      }
    },
    "50000009": {
      "category": "electronics",
      "featured": true,
      "name": "Smart TV",
      "description": "Ultra HD smart television with built-in streaming apps.",
      "variants": [
        { "sku": 3007, "spec": "1080p", "price": 199, "quantity": 70 }, // 60 -> 70
        { "sku": 3008, "spec": "4K", "price": 399, "quantity": 40 }  // 30 -> 40
      ]
    },
  }
}

✅ Inventories for in-stock variants are incremented directly on the server.

Combine multiple filters

Filters can be chained with AND / OR with each expression pulling data from the current iteration’s element into a different loop variable.

Example: Select variants that are in stock and have price < 50.

Exp filterOnCheapInStock = Exp.and(
    Exp.gt(
        MapExp.getByKey(MapReturnType.VALUE, Exp.Type.INT,
            Exp.val("quantity"),
            Exp.mapLoopVar(LoopVarPart.VALUE)),
        Exp.val(0)),
    Exp.lt(
        MapExp.getByKey(MapReturnType.VALUE, Exp.Type.INT,
            Exp.val("price"),
            Exp.mapLoopVar(LoopVarPart.VALUE)),
        Exp.val(50)));
// Operation
Record record = client.operate(null, key,
    CdtOperation.selectByPath("catalog", Exp.SELECT_MATCHING_TREE,
        CTX.allChildren(),
        CTX.allChildrenWithFilter(filterOnFeatured),
        CTX.mapKey(Value.get("variants")),
        CTX.allChildrenWithFilter(filterOnCheapInStock)));


System.out.println(record.getList("catalog"));

Expected output:

{
  "inventory": {
    "10000001": {
      "variants": {
        "2001": { "price": 25, "quantity": 100, "size": "S" },
        "2003": { "price": 27, "quantity": 50, "size": "L" }
      }
    },
    "50000006": { "variants": {} },
    "50000009": { "variants": {} }
  }
}

✅ Only items are returned which have price < 50 and quantity > 0.

❌ Item 10000002, Casual Polo Shirt, excluded (featured=false).

❌ Item 50000006, Laptop Pro 14, excluded (quantity=0).

❌ Item 50000009, Smart TV, both variants excluded (price > 50).

NO_FAIL: tolerate malformed product

If we add this item to the inventory bin:

"10000003": {
  "category": "clothing",
  "featured": true,
  "name": "Hooded Sweatshirt",
  "description": "Warm fleece hoodie with front pocket and adjustable hood.",
  "variants": "no variant"
}

The dataset now includes item 10000003 with variants: “no variant” (a string). Any traversal that reaches variants and then tries to treat it as a Map/List will hit a type mismatch and throw an error unless SelectFlags.NO_FAIL.flag is set.

// Operation
Record noFailResponse = client.operate(null, key,
      CdtOperation.selectByPath("catalog", Exp.SELECT_MAP_KEY | Exp.SELECT_NO_FAIL,
          CTX.allChildren(),
          CTX.allChildrenWithFilter(filterOnFeatured),
          CTX.mapKey(Value.get("variants")),
          CTX.allChildrenWithFilter(filterOnVariantInventory)
      )
);
System.out.println(noFailResponse.getList("catalog"));

  • malformed_product.variants is “no variant”.

  • With NO_FAIL, malformed_product is excluded silently because variants was “no variant”.

Expected output:

Same as the corresponding non-NO_FAIL query, omitting any items from malformed_product.

["2001","2003"]

❌ Item 10000003 skipped silently because variants was a string.

Handle errors gracefully

Path Expression operations can fail for several reasons. Always wrap operations in error handling to provide a good user experience.

Common error scenarios:

  • Target bin doesn’t exist or isn’t a CDT
  • Type mismatch in filter expression (without NO_FAIL)
  • Server timeout during complex traversals
import com.aerospike.client.AerospikeException;
import com.aerospike.client.ResultCode;


try {
  Record record = client.operate(null, key,
    CdtOperation.selectByPath("catalog", Exp.SELECT_MATCHING_TREE,
      CTX.allChildren(),
      CTX.allChildrenWithFilter(filterOnFeatured),
      CTX.mapKey(Value.get("variants")),
      CTX.allChildrenWithFilter(filterOnVariantInventory)));
  // Success - process the filtered results
  System.out.println(record.getList("catalog"));
} catch (AerospikeException e) {
  switch (e.getResultCode()) {
    case ResultCode.BIN_TYPE_ERROR:
    case ResultCode.OP_NOT_APPLICABLE:
      // The bin exists but isn't a Map or List - can't traverse it
      System.err.println("Bin is not a Map or List");
      break;
    case ResultCode.PARAMETER_ERROR:
       // The filter expression is malformed or uses wrong types
       System.err.println("Invalid expression in filter");
      break;
    default:
        // Unexpected error (network, timeout, etc.) - propagate it
        throw e;
  }
}
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