neo4j

Neo4j - Transactional HTTP endpoint

要讀取、更新、刪除和建立neo4j的node或relationship，可以透過embedded或http的方式，去針對database去操作。

使用http的方式，基本上就是呼叫rest api，db server會依照不同的狀況回傳response status code，同樣也會依照get、post、put、delete去告訴db server，目前要處理方式。

然而neo4j中，提供了很多http的api，可以針對db操作，像是rest api transactional或Cypher這類的neo4j rest api。

Embedded graph database

透過embedded的方式，會直接在嵌入在你所撰寫的project裡，指定好要儲存的db的path，換句話說，檔案會儲存在server的local端，與以往的mysql、mongodb透過socket的方式不同，有點類似sqlite。

使用embedded的方式，大概會如下方(參考官方)：

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GraphDatabaseService graphDb = new GraphDatabaseFactory().newEmbeddedDatabase( "/your_db_path" );

try {
     Transaction tx = graphDb.beginTx();

     Node firstNode = graphDb.createNode();
     firstNode.setProperty( "message", "Hello world" );
     System.out.print( firstNode.getProperty( "message" ) );

     // Database operations go here
     tx.success();

 }catch( Exception e ){

     //do something
 }

Transactional HTTP endpoint

在這簡單介紹Transactional HTTP endpoint，首先neo4j的每個query都會經由transaction機制去處理，所以可以透過已知的transaction的id，下一整串的query，最後在決定要rollback或commit，如果太久沒有commit，neo4j會有個timeout時間(預設60 sec)，就會取消先前的query結果。

Begin a transaction

建立一個transaction，之後可以沿用這個transaction的id，去執行一連串的query。

官方Example:

Request headers:

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POST http://localhost:7474/db/data/transaction
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ {
    "statement" : "CREATE (n {props}) RETURN n",
    "parameters" : {
      "props" : {
        "name" : "My Node"
      }
    }
  } ]
}

statements可以一次下多筆query，statement會參照parameters的參數。

Response headers:

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201: Created
Content-Type: application/json
Location: http://localhost:7474/db/data/transaction/7

Response json data:

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{
  "commit" : "http://localhost:7474/db/data/transaction/7/commit",
  "results" : [ {
    "columns" : [ "n" ],
    "data" : [ {
      "row" : [ {
        "name" : "My Node"
      } ]
    } ]
  } ],
  "transaction" : {
    "expires" : "Mon, 03 Feb 2014 13:26:48 +0000"
  },
  "errors" : [ ]
}

每個response都會回傳一個transaction的expires，這個expires的指的就是transaction的存活時間，而commit這個field包含transaction的id，這上面這範例id為7。

Execute statements in an open transaction

使用先前建立transaction，依照transaction的id，繼續執行query，若是transaction失效，最後會取得到error messsage。

官方Example:

Request headers:

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POST http://localhost:7474/db/data/transaction/7
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ {
    "statement" : "CREATE n RETURN n"
  } ]
}

Response headers:

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200: OK
Content-Type: application/json

Response json data:

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{
  "commit" : "http://localhost:7474/db/data/transaction/7/commit",
  "results" : [ {
    "columns" : [ "n" ],
    "data" : [ {
      "row" : [ {
      } ]
    } ]
  } ],
  "transaction" : {
    "expires" : "Mon, 03 Feb 2014 13:26:48 +0000"
  },
  "errors" : [ ]
}

Execute statements in an open transaction in REST format for the return

在還沒commit之前，只有node會被建立，而建立的properties或relationship等的…，一直到commit之後，在database中才有辦法query的到。而REST這個參數，可以幫助你取得目前node間的狀況，response會回傳各種想要查詢的rest api。

官方Example:

Request headers:

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POST http://localhost:7474/db/data/transaction/1
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ {
    "statement" : "CREATE n RETURN n",
    "resultDataContents" : [ "REST" ]
  } ]
}

Response headers:

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200: OK
Content-Type: application/json

Response json data:

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{
  "commit" : "http://localhost:7474/db/data/transaction/1/commit",
  "results" : [ {
    "columns" : [ "n" ],
    "data" : [ {
      "rest" : [ {
        "paged_traverse" : "http://localhost:7474/db/data/node/12/paged/traverse/{returnType}{?pageSize,leaseTime}",
        "labels" : "http://localhost:7474/db/data/node/12/labels",
        "outgoing_relationships" : "http://localhost:7474/db/data/node/12/relationships/out",
        "traverse" : "http://localhost:7474/db/data/node/12/traverse/{returnType}",
        "all_typed_relationships" : "http://localhost:7474/db/data/node/12/relationships/all/{-list|&|types}",
        "property" : "http://localhost:7474/db/data/node/12/properties/{key}",
        "all_relationships" : "http://localhost:7474/db/data/node/12/relationships/all",
        "self" : "http://localhost:7474/db/data/node/12",
        "properties" : "http://localhost:7474/db/data/node/12/properties",
        "outgoing_typed_relationships" : "http://localhost:7474/db/data/node/12/relationships/out/{-list|&|types}",
        "incoming_relationships" : "http://localhost:7474/db/data/node/12/relationships/in",
        "incoming_typed_relationships" : "http://localhost:7474/db/data/node/12/relationships/in/{-list|&|types}",
        "create_relationship" : "http://localhost:7474/db/data/node/12/relationships",
        "data" : {
        }
      } ]
    } ]
  } ],
  "transaction" : {
    "expires" : "Mon, 03 Feb 2014 13:26:44 +0000"
  },
  "errors" : [ ]
}

Reset transaction timeout of an open transaction

transaction是會過期的，要解決這問題，只要向http://localhost:7474/db/data/transaction/1發送，時效性就會自動延長，若不想下query，只想延長時效。可以發送一個不帶statements內容的的query。

Request headers:

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POST http://localhost:7474/db/data/transaction/1
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ ]
}

Commit an open transaction

要確定存入database，只要commit目前的transaction即可。

Request:

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POST http://localhost:7474/db/data/transaction/4/commit
Accept: application/json; charset=UTF-8
Content-Type: application/json

Rollback an open transaction

要取消之前transaction中執行過的query，只要使用rollback即可。

Request:

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DELETE http://localhost:7474/db/data/transaction/3
Accept: application/json; charset=UTF-8

Begin and commit a transaction in one request

如果要執行query後，馬上commit，可以直接透過/db/data/transaction/commit。

Request headers:

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POST http://localhost:7474/db/data/transaction/commit
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ {
    "statement" : "CREATE n RETURN id(n)"
  } ]
}

Return results in graph format

如果想要查詢節點的圖形結構關係，可以在resultDataContents加入graph這個參數。

Request headers:

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POST http://localhost:7474/db/data/transaction/commit
Accept: application/json; charset=UTF-8
Content-Type: application/json

Request json data:

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{
  "statements" : [ {
    "statement" : "CREATE ( bike:Bike { weight: 10 } )CREATE ( frontWheel:Wheel { spokes: 3 } )CREATE ( backWheel:Wheel { spokes: 32 } )CREATE p1 = bike -[:HAS { position: 1 } ]-> frontWheel CREATE p2 = bike -[:HAS { position: 2 } ]-> backWheel RETURN bike, p1, p2",
    "resultDataContents" : [ "row", "graph" ]
  } ]
}

Response headers:

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200: OK
Content-Type: application/json

Response json data:

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{
  "results" : [ {
    "columns" : [ "bike", "p1", "p2" ],
    "data" : [ {
      "row" : [ {
        "weight" : 10
      }, [ {
        "weight" : 10
      }, {
        "position" : 1
      }, {
        "spokes" : 3
      } ], [ {
        "weight" : 10
      }, {
        "position" : 2
      }, {
        "spokes" : 32
      } ] ],
      "graph" : {
        "nodes" : [ {
          "id" : "17",
          "labels" : [ "Wheel" ],
          "properties" : {
            "spokes" : 3
          }
        }, {
          "id" : "16",
          "labels" : [ "Bike" ],
          "properties" : {
            "weight" : 10
          }
        }, {
          "id" : "18",
          "labels" : [ "Wheel" ],
          "properties" : {
            "spokes" : 32
          }
        } ],
        "relationships" : [ {
          "id" : "9",
          "type" : "HAS",
          "startNode" : "16",
          "endNode" : "17",
          "properties" : {
            "position" : 1
          }
        }, {
          "id" : "10",
          "type" : "HAS",
          "startNode" : "16",
          "endNode" : "18",
          "properties" : {
            "position" : 2
          }
        } ]
      }
    } ]
  } ],
  "errors" : [ ]
}

Python example

上述對照的request json data或request headers可參考底下的範例，每個語言使用方式差不多。

dependency

install

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sudo pip install requests

code

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import requests, json       
                            
headers = {                 
    "Accept": "application/json; charset=UTF-8",
    "Content-Type": "application/json"
}                           
                            
data = {                    
  "statements" : [ {        
    "statement" : "MATCH (n {name: {name}}) RETURN n",
    "parameters" : {        
      "name":"Sparrow"   
    }                       
  } ]                       
}                           
                            
url = "http://localhost:7474/db/data/transaction"
                            
req = requests.post( url , data = json.dumps( data ), headers = headers )                                                                             
                            
print req.text

可參照官方的Transactional HTTP endpoint，和rest api回傳的status code。