Data Modification Statements

The GSQL language provides full support for vertex and edge insertion, deletion, and attribute update.

Each query is considered one transaction. Therefore, modifications to the graph data do not take effect until the entire query is completed (committed). Accordingly, any modification statement does not affect any other statements inside the same query.

Query-body DELETE Statement

The query-body DELETE statement deletes a given set of edges or vertices.This statement can only be used as a query-body statement. Deletion at the DML-sub level is served by the DML-sub DELETE statement.

The GSQL DELETE operation is a cascading deletion. If a vertex is deleted, then all edges which connect to it are automatically deleted as well.

Syntax

EBNF
queryBodyDeleteStmt := DELETE alias FROM pathPattern [whereClause]

The FROM clause in the DELETE statement follows the same rules as those in the FROM clause in a SELECT statement. However, the FROM clause in the DELETE statement only supports 1-hop, instead of multiple hops in the SELECT statement.

The WHERE clause can filter the items in the path pattern.

Examples

Below are two examples, one for deleting vertices and one for deleting edges.

Deleting vertices
CREATE QUERY delete_ex() FOR GRAPH Work_Net {
    // Delete all "Person" vertices with location equal to "us"

    S = {Person.*};
    DELETE s FROM S:s
        WHERE s.location_id == "us";
}
Deleting edges
CREATE QUERY delete_ex_2() FOR GRAPH Work_Net {
    // Delete all "Works_For" edges where the person's location is "us"

    S = {Person.*};
    DELETE e FROM S:s -(Works_For:e)- Company:t
        WHERE s.location_id == "us";
}

The following query can be used to observe the effect of the delete statements. This query counts the person vertices who work in the US and the Works_For edges for persons in the US. When the initial Work_Net test data loaded, there are 5 persons and 9 Works_For edges for locationId = "us".

If query delete_ex2 is run, there are 5 persons but 0 Works_For edges. Next, if the deleteEx query is run, the works_at_US query then finds 0 persons and 0 Works_For edges.

Query to check the results of deleteEx and deleteEx2
CREATE QUERY count_at_location(STRING loc) FOR GRAPH Work_Net {
    SetAccum<EDGE> @@sel_edge;
    Start = {Person.*};

    SV = SELECT s FROM Start:s
        WHERE s.location_id == loc;
    PRINT SV.size() AS num_vertices;

    SE = SELECT s FROM Start:s -(Works_For:e)- Company:t
        WHERE s.location_id == loc
        ACCUM @@sel_edge += e;
        PRINT @@sel_edge.size() AS num_edges;
}

Below are the results of the queries in sequence:

  • Query

  • Results

deleteEx.run
RUN QUERY count_at_location("us")
RUN QUERY delete_ex2()
RUN QUERY count_at_location("us")
RUN QUERY deleteEx()
RUN QUERY count_at_location("us")
Results from DeleteEx Example
// Before any deletions
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"numVertices": 5},
    {"numEdges": 9}
  ]
}
// Delete edges
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": []
}
// After deleting edges
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"numVertices": 5},
    {"numEdges": 0}
  ]
}
// Delete vertices
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": []
}
// After deleting vertices
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"numVertices": 0},
    {"numEdges": 0}
  ]
}

DML-sub DELETE Statement

DML-sub DELETE is a DML-sub statement which deletes one vertex or edge each time it is called. Deletion at the query-body level is served by the Query-body DELETE statement.

In practice, this statement resides within the body of a SELECT…​ACCUM/POST-ACCUM clause, so it is called once for each member of a selected vertex set or edge set.

The GSQL DELETE operation is a cascading deletion. If a vertex is deleted, then all edges which connect to it are automatically deleted as well.

The ACCUM clause iterates over an edge set, which can encounter the same vertex multiple times. If you wish to delete a vertex, it is best practice to place the DML-sub DELETE statement in the POST-ACCUM clause rather than in the ACCUM clause.

Syntax

EBNF
dmlSubDeleteStmt := DELETE "(" alias ")"

Examples

The following example uses and modifies the graph data for Social_Net.

DELETE within ACCUM vs. POST-ACCUM
CREATE QUERY delete_posts(VERTEX<Person> seed) FOR GRAPH Social_Net {
	// Remove any post vertices posted by the given user

    start = {seed};

	/* Best practice is to delete a vertex in a POST-ACCUM, which only
	 occurs once for each vertex v, guaranteeing that a vertex is not
	 deleted more than once */
	post_accum_deleted_posts = SELECT v FROM start -(Posted>:e)- Post:v
        POST-ACCUM DELETE (v);

	/* Possible, but not recommended as the DML-sub DELETE statement occurs
	 once for each edge of the vertex v */
	accum_deleted_posts = SELECT v FROM start -(Posted>:e)- Post:v
        ACCUM DELETE (v);
}

// Need a separate query to display the results, because deletions don't take effect during the query.
CREATE QUERY select_user_posts(VERTEX<Person> seed) FOR GRAPH Social_Net {
    start = {seed};

    user_posts = SELECT v FROM start -(Posted>:e)- Post:v;
    PRINT user_posts;
}

For example, the following sequence of select_user_posts and delete_posts queries

deletePosts.run
RUN QUERY select_user_posts("person3")
RUN QUERY delete_posts("person3")
RUN QUERY select_user_posts("person3")

will produce the following result:

Results from DeletePosts Example
// Before the deletion
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"userPosts": [{
    "v_id": "2",
    "attributes": {
      "postTime": "2011-02-03 01:02:42",
      "subject": "query languages"
    },
    "v_type": "post"
  }]}]
}
// Deletion; no output results requested at this point
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": []
}
// After the deletion
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [{"userPosts": []}]
}

INSERT INTO Statement

The INSERT INTO statement adds edges or vertices to the graph. When the ID value(s) for the inserted vertex/edge match those of an existing vertex/edge, the new values will overwrite the old values. To insert an edge, its endpoint vertices must already exist, either before running the query or inserted earlier in that query. The INSERT INTO statement can be used as a query-body-level statement or a DML-sub statement.

Like any other data modification in a query, the insertion does not take effect until the entire query is completed.

insertStmt := insertVertexStmt | insertEdgeStmt
insertVertexStmt := INSERT INTO (vertexType | name)
                 ["(" PRIMARY_ID ["," attrName]* ")"]
                 VALUES "(" ( "_" | expr ) ["," ("_" | expr)]*] ")"
insertEdgeStmt   := INSERT INTO (edgeType | EDGE name)
                 ["("
                    FROM "," TO “,”
                    [(DISCRIMINATOR "(" attrName ("," attrName)* ")") ]
                 ")"]
                 VALUES "(" ( "_" | expr ) [vertexType]
                 ["," ( "_" | expr ) [vertexType] ["," ("_" | expr)]*] ")"

There are two options for specifying the attributes of the vertex or edge type for the values provided:

  • Provide a value for the ID(s) and then each attribute, in the canonical order for the vertex or edge type. In this case, it is not necessary to explicitly name the attributes, since it is assumed that every attribute is being referenced, in order.

    INSERT with implicit attribute names
    INSERT INTO vertex_or_edge_type VALUES (full_list_of_parameter_values)

  • Name the specific attributes to be set, and then provide a corresponding list of values. The attributes can be in any order, with the exception that the IDs must come first. That is, to insert a vertex, the first attribute name must be PRIMARY_ID. To insert an edge, the first two attribute names must be FROM and TO.

    INSERT with explicit attribute names
    INSERT INTO vertex_type (PRIMARY_ID, specified_attributes)
VALUES (ID, values_for_specified_attributes)

INSERT INTO edge_type (FROM, TO, specified_attributes)
VALUES (value_for_from_vertex, value_for_to_vertex, (1)
    values_for_specified_attributes)
    1 value_for_from_vertex and value_for_to_vertex can either be the ID of the vertex followed by the vertex type, separated by a space or a vertex variable.

    For each attribute value, provide either an expression expr or , which means the default value for that attribute type. The optional _name which follows the first two (id) values is to specify the source vertex type and target vertex type, if the edge type had been defined with wildcard vertex types.

Query-Body INSERT

The following query illustrates query-body level INSERT statements: insert new Company vertices and Works_For edges into the Works_Net graph.

INSERT statement
CREATE QUERY insert_ex(STRING name, STRING name2, STRING name3, STRING comp) FOR GRAPH Work_Net {
    /* Vertex insertion
     Adds 2 'Company' vertices. One is located in the USA, and a sister company in Japan.
    Company:
     Company(PRIMARY_ID client_id STRING, id STRING, country STRING) */
    INSERT INTO Company VALUES ( comp, comp, "us" );
    INSERT INTO Company (PRIMARY_ID, country) VALUES ( comp + "_jp", "jp" );

    /* Edge insertion
    Adds a 'Works_For' edge from person 'name' to the company 'comp', filling in default
    values for startYear (0), startMonth (0), and fullTime (false).
    Works_For:
    Works_For(FROM person, TO company, startYear INT, startMonth INT, fullTime BOOL) */
    INSERT INTO Works_For VALUES (name Person, comp Company, _, _, _);

    /* Adds a 'Works_For' edge from person 'name2' to the company 'comp', filling in
        default values for startMonth (0), but specifying values for startYear and
        fullTime. */
    INSERT INTO Works_For (FROM, TO, start_year, full_time) VALUES (name2 Person, comp Company, 2017, true);

    /* Adds a 'Works_For' edge from person 'name3' to the company 'comp', filling in
    default values for startMonth (0), and fullTime (false) but specifying a value
    for startYear (2017). */
    INSERT INTO Works_For (FROM, TO, start_year) VALUES (name3 Person, comp Company, 2000 + 17);
}

The following query can be used to check the effect of the previous query. Prior to running insertEx, running whoWorksForCompany("gsql") will find 0 companies called "gsql" and 0 Works_For edges for company "gsql".

If we then run the query insertEx("tic", "tac", "toe", "gsql"), then insertEx("gsql") will find a company called "gsql" and another one called "gsql_jp". Moreover, it will find 3 edges, tic, tac, and toe, with different values for the startMonth, startYear, and fullTime parameters.

Query to check the results of insertEx
CREATE QUERY who_works_for_company(STRING comp) FOR GRAPH Works_Net {
    SetAccum<EDGE> @@set_edge;

    Comps = {Company.*};
    PRINT Comps[Comps.id];   // output api v2

    Pers = {Person.*};
    S = SELECT s
        FROM Pers:s -(Works_For:e)- :t
        WHERE t.id == comp
        ACCUM @@set_edge += e;
    PRINT @@set_edge;
}

To insert an edge with a discriminator value specified, use the DISCRIMINATOR keyword to specify the discriminator attributes and specify the values in order. For example, the following statement inserts an edge between two vertices with the discriminator values being 2019 and 01, respectively.

INSERT INTO Study_At (FROM, TO, DISCRIMINATOR(class_year, class_month))
    VALUES ("Alice" Person, "CMU" University, (2019, 01));

DML-sub INSERT

The following example shows a DML-sub level INSERT. Because the statement applies to all companies, several vertices will be inserted.

DML-sub INSERT statement
CREATE QUERY add_new_child_company(STRING name) FOR GRAPH Work_Net {
    // Adds a child company of a given company name. The new child company is in japan

    all_companies = {Company.*};
    X = SELECT s
        FROM all_companies:s
        WHERE s.id == name
        ACCUM
            INSERT INTO Company VALUES ( name + "_jp", name + "_jp", "jp" );
}

// Adds separate query to list the companies, before and after the insertion
CREATE QUERY list_company_names(STRING country_filter) FOR GRAPH Works_Net {
  all_companies = {Company.*};
  C = SELECT s
      FROM all_companies:s
      WHERE s.country == country_filter;

  PRINT C.size() AS num_companies;
  PRINT C;
}

Example

The following queries add a child company in Japan to the US-based company company3. List all the Japan-based companies before and after the insertion.

addNewChildCompany.run
RUN QUERY list_company_names("jp")
RUN QUERY add_new_child_company("company4")
RUN QUERY list_company_names("jp")
Results from addNewChildCompany Example
# Before insertion
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"numCompanies": 1},
    {"C": [{
      "v_id": "company3",
      "attributes": {
        "country": "jp",
        "id": "company3"
      },
      "v_type": "company"
    }]}
  ]
}
# insert company "company4_jp"
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": []
}
# after insertion
{
  "error": false,
  "message": "",
  "version": {
    "edition": "developer",
    "schema": 0,
    "api": "v2"
  },
  "results": [
    {"numCompanies": 2},
    {"C": [
      {
        "v_id": "company3",
        "attributes": {
          "country": "jp",
          "id": "company3"
        },
        "v_type": "company"
      },
      {
        "v_id": "company4_jp",
        "attributes": {
          "country": "jp",
          "id": "company4_jp"
        },
        "v_type": "company"
      }
    ]}
  ]
}

UPDATE Statement

The UPDATE statement updates the attributes of vertices or edges.

Syntax

EBNF
updateStmt := UPDATE alias FROM pattern SET dmlSubStmtList [whereClause]
pattern := (vertexPattern | edgePattern)

The set of vertices or edges to update is described in the FROM clause, following the same rules as the FROM clause in a SELECT statement. In the SET clause, the dmlSubStmtList contains assignment statements to update the attributes of a vertex or edge. Both simple base type attributes and collection type attributes can be updated. These assignment statements use the vertex or edge aliases declared in the FROM clause. The optional WHERE clause supports boolean conditions to filter the items in the vertex set or edge set.

Examples

UPDATE statement example
CREATE QUERY update_ex() FOR GRAPH Work_Net  {
    // This query changes all "Person" vertices with location equal to "us" to "USA"
    S = {Person.*};

    UPDATE s FROM S:s
    SET s.location_id = "USA",  // simple base type attribute
        s.skill_list = [1,2,3]  // collection-type attribute
    WHERE s.location_id == "us";

    // The update cannot become effective within this query, so PRINT S still show "us".
    PRINT S;
}

The UPDATE statement can only be used as a query-body-level statement. However, DML-sub level updates are still possible by using other statement types. A vertex attribute’s value can be updated within the POST-ACCUM clause of a SELECT block by using the assignment operator (=); An edge attribute’s value can be updated within the ACCUM clause of a SELECT block by using the assignment operator. In fact, the UPDATE statement is equivalent to a SELECT statement with ACCUM and/or POST-ACCUM to update the vertex or edge attribute values.

Updating a vertex’s attribute value in an ACCUM clause is not allowed, because the update can occur multiple times in parallel, and possibly result in a non-deterministic value. If the vertex attribute value update depends on an edge attribute value, use the vertex-attached accumulators to save the value and update the vertex attribute’s value in the POST-ACCUM clause.

The query below uses a SELECT statement instead of an UPDATE statement and performs the same update as the query above.

CREATE QUERY update_ex2() FOR GRAPH Work_Net  {
    S = {Person.*};

    X = SELECT s
        FROM S:s
        WHERE S.location_id == "USA"
        POST-ACCUM S.location_id = "us",
            S.skill_list = [3,2,1];
    PRINT S;
}

Assignment statements

In addition to UPDATE statements and SELECT statements, a simple assignment statement at the query-body level can be used to update the attribute value of a single vertex or edge, if the vertex or edge has been assigned to a variable or parameter.

Update by assignment
// Change the given person's location
CREATE QUERY update_by_assignment(VERTEX<Person> v, STRING new_location)
    FOR GRAPH Work_Net {
  v.location_id = new_location;
}