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BLOB

BLOBs represent binary streams stored in an EXTERNAL storage (local files system, distributed file system, etc) and can be consumed in streamming manner (only offer new bytes on calling next()). Unlike BLOBs, byte arrays are always stored INSIDE a Neo4j store, and often be fetched as a whole object (thus large byte arrays are not suitable to be stored in Neo4j).

to use BLOB, graiph-blob-impl (https://github.com/grapheco/graiph-blob-commons) artifact is required:

<dependency>
    <groupId>org.grapheco</groupId>
    <artifactId>graiph-blob-api</artifactId>
    <version>0.1.0</version>
</dependency>

A BLOB contains two properties: length and mimeType:

trait Blob extends Comparable[Blob] {
  val length: Long;
  val mimeType: MimeType;
  ...
}

BlobFactory provides serveral methods to build a blob object:

  • def fromBytes(bytes: Array[Byte]): Blob
  • val EMPTY: Blob
  • def fromInputStreamSource(iss: InputStreamSource, length: Long, mimeType: Option[MimeType] = None): Blob
  • def fromFile(file: File, mimeType: Option[MimeType] = None): Blob
  • def fromHttpURL(url: String): Blob
  • def fromURL(url: String): Blob

To consume content of a BLOB, use offerStream:

  blob.offerStream { is =>
    is.read();
    ...
  }

It is unrecommended to use Blob.toByteArray() to avoid large memory cost.

writing & reading blobs

  //create a node
  val node1 = db.createNode();

  node1.setProperty("name", "bob");
  node1.setProperty("age", 40);

  //with a blob property
  node1.setProperty("photo", BlobFactory.fromFile(new File("./testdata/test.png")));
  ...

The code shown above creates a graph node with a photo property, which is of a blob type, and its content comes from the local file ./testdata/test.png.

To read a blob from Neo4j database:

  //reload database
  val db2 = openDatabase();
  val tx2 = db2.beginTx();
  //get first node
  val it = db2.getAllNodes().iterator();
  val v1: Node = it.next();
  val blob = v1.getProperty("photo").asInstanceOf[Blob];

For more example code, see https://github.com/bluejoe2008/neo4j-blob/blob/blob-support/community/neo4j-blob/neo4j-blob-test/src/test/scala/GraphDbBlobTest.scala

blob in Cypher

BlobLiteral is defined in Cypher grammar in form of: <schema://path>

Following schema is ok:

  • file: local files in Neo4j server
  • http
  • https
  • ftp
  • base64: path should be a BASE64 encoding string, for example: <base64://dGhpcyBpcyBhbiBleGFtcGxl> represents a string with content this is an example

Next code illustrates how to use blob in Cypher query:

//create a node
CREATE (n:PERSON { name: "bluejoe", photo: <https://avatars0.githubusercontent.com/u/2328905?s=460&v=4> });

Retrieving a BLOB property:

val result = tx.run("MATCH (n:PERSON) where n.name='bluejoe' return n");
val blob = result.get(0).asBlob

For more example code, see https://github.com/bluejoe2008/neo4j-blob/blob/blob-support/community/neo4j-blob/neo4j-blob-test/src/test/scala/BoltCypherTest.scala

blob functions

Serveral functions are defined as Cypher UDFs:

  • Blob.fromFile(filePath: String): Blob
  • Blob.fromURL(url: String): Blob
  • Blob.fromString(text: String, encoding: String): Blob
  • Blob.fromUTF8String(text: String): Blob
  • Blob.fromBytes(bytes: Array[Byte]): Blob
  • Bytes.guessType(bytes: Array[Byte]): String
  • Blob.guessType(blob: Blob): String
  • Blob.empty(): Blob
  • Blob.len(blob: Blob): Long
  • Blob.toString(blob: Blob, encoding: String): String
  • Bytes.fromFile(filePath: String): Array[Byte]
  • Blob.toUTF8String(blob: Blob): String
  • Blob.toBytes(blob: Blob): Array[Byte]
  • Blob.mime(blob: Blob): String, get mime type, e.g. image/png
  • Blob.mime1(blob: Blob): String, get major mime type, e.g. image
  • Blob.mime2(blob: Blob): String, get minor mime type, e.g. png
  • Blob.is(blob: Blob, mimeType: String): Boolean, determine if the blob is kind of specified mime type

These functions are registered automatically on start, so be free to use them.