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v4.0
    v4.0

    Alias System

    Structure Type of Alias

    Alias is to name the data columns generated during the execution of UQL, so that the data columns can be called in the subsequent UQL statment.

    There are 6 structure types a alias can represent:

    Structure Type
    Definition Example
    Alias Example
    Data Structure Example
    NODE n(as nodes).e().n() nodes {id: , uuid: , schema: , values: {...}}
    EDGE n().e({time > prev_e.time})[3].n() prev_e {uuid: , schema: , from: , from_uuid: , to: , to_uuid: , values: {...}}
    PATH n().e().n() as paths paths {nodes: [<NODE>, <NODE>, ...], edges: [<EDGE>, <EDGE>, ...]}
    ATTR uncollect ["Alice","Paal"] as name
    uncollect ["1993-06-12","1989-03-26"] as birthday
    name
    birthday
    Atomic data without internal structure, such as string, number and so on
    ARRAY n().e()[3].n() as paths
    with pedges(paths) as edgeUUIDs

    edgeUUIDs
    [<ATTR>, <ATTR>, ...]
    TABLE uncollect ["Alice","Paal"] as name
    uncollect ["1993-06-12","1989-03-26"] as birthday
    with table(name, birthday) as record


    record
    {headers: [], table_rows: [<ARRAY>, <ARRAY>, ...]}

    Not defining alais for data stream generatd during the execution of UQL, or not calling an alias defined could have negative effect on the legality of UQL. Please avoid missing defining alias or defining alias that is not called later on.

    Custom Alias

    A custom alias is defined by the user. The nodes, paths, name, birthday, edgeUUIDs and record in the previous table are all custom aliases.

    Rules of defining a custom alias:

    • Use alias keyword as;
    • Please refer to chapter Basic Concepts for the naming conventions of alias
      • Note that custom alias also accepts only 1 character.
      • Cannot have the same name with existing custom alias, nor can system reserved words be used (see chapter Basic Concepts for details).
      • Try to avoid duplicate names with the property names of the nodes or edges to be used in the same statement; if this is not possible, system alias this may be used to disambiguate if necessary.

    Structure types a custom alias may represent: NODE, EDGE, PATH, ATTR, ARRAY, TABLE

    Life cycle of a customer alias: anywhere after the alias is defined.

    In case an alias cannot be called by a statment far from where this alias is defined, re-defining alias for that data column in a WITH clause my solve the problem.

    System Alias

    A system alias is defined by the system. There are 3 system aliases, prev_n, prev_e and this. They can be used directly without definition:

    System Alias Meaning Structure Type Life Cycle
    this Current node or edge NODE or EDGE In any filter
    prev_n The previous node of the current node or edge NODE In the filter of any baisc template
    this The previous edge of the current node or edge EDGE In the filter of any baisc template

    Please read chapter Template for details on prev_n and prev_e.

    In practical applications, this is rarely used unless to eliminate any ambiguity; ambiguity occurs when the names of the node/edge's property and the custom alias are repeated, this has to be used in this case if there is a need to refer to the property of node/edge.

    ... as balance
    find().nodes({this.balance > 5000})
    

    Note: In this example, this.balance in nodes() represents the balance property of the current node; since the custom alias defined in the previous statement is still valid in the current statement, using balance in nodes() directly conflicts with the name of node's property balance, so that this is used.

    Call an Alias

    When calling the alias of ATTR, ARRAY or TABLE, the complete data structure will be called.

    When calling the alias of NODE, EDGE or PATH, use different call format to either call the JSON structure with complete KVs, or the JSON with partial KVs, or just one KV from the JSON.

    Suppose that nodes, edges and paths are aliases of NODE, EDGE or PATH, below call formats are supported:

    The alias of NODE, EDGE and PATH in the RETURN clause carries schema and system properties (_uuid, _id, _from, _to, _from_uuid, _to_uuid) of nodes and/or edges by default, this information covers the table below.

    Call Format
    Call Type
    Specification Meaning
    nodes NODE Call in any statement Nodes that do not carry any custom properties
    nodes.<property> ATTR Call in any statement A property of the nodes (or empty if the property does not exist; the same below)
    nodes.@ ATTR Call in any statement Schemas of the nodes
    nodes{<property>, ...} NODE Call in RETURN clause Nodes that carry several custom properties
    nodes{*} NODE Call in RETURN clause Nodes that carry all custom properties
    edges EDGE Call in any statement Edges that do not carry any custom properties
    edges.<property> ATTR Call in any statement A property of the edges
    edges.@ ATTR Call in any statement Schemas of the edges
    edges{<property>, ...} EDGE Call in RETURN clause Edges that carry several custom properties
    edges{*} EDGE Call in RETURN clause Edges that carry all custom properties
    paths PATH Call in any statement Paths that do not carry any custom properties of its nodes and edges
    paths{<property>, ...}{<property>, ...} PATH Call in RETURN clause Paths that carry several custom properties of its nodes and edges
    paths{*}{<property>, ...} PATH Call in RETURN clause Paths that carry all custom properties of its nodes and several custom properties of its edges
    paths{<property>, ...}{*} PATH Call in RETURN clause Paths that carry several custom properties of its nodes and all custom properties of its edges
    paths{*} PATH Call in RETURN clause Paths that carry all custom properties of its nodes and edges

    User may gradually comprehend the concepts above as continue reading.

    Read chapter Data Stream, Clause for the detailed description of RETURN.

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