Alias and Data Structure
Alias exists to name the data stream generated during or at the end of the execution of UQL, so that the data stream can be called in the subsequent UQL statement.
There are 6 data structures an alias can represent:
Data Structure |
Definition Example | Alias in Example |
Data Structure in RETURN |
|---|---|---|---|
| NODE | find().nodes() as nodes | nodes | {id: , uuid: , schema: , values: {...}} |
| EDGE | find().edges() as edges | edges | {uuid: , schema: , from: , from_uuid: , to: , to_uuid: , values: {...}} |
| PATH | n().e().n() as paths | paths | {nodes: [<NODE>, <NODE>, ...], edges: [<EDGE>, <EDGE>, ...]} |
| ATTR | ... as nodes with year(nodes.birthday) as attr1, nodes.name as arrt2, nodes.@ as arrt3 |
attr1, attr2, attr3 | Atomic value without internal structure, such as string, number and so on |
| ARRAY | ... as paths with pedges(paths) as array |
array | [<ATTR>, <ATTR>, ...] |
| TABLE | ... as nodes with table(nodes.name, nodes.birthday) as table |
table | {headers: [...], table_rows: [<ARRAY>, <ARRAY>, ...]} |
Omission of defining alias for a newly generated data, or defining an alias that is never called, both could induce negative effect on the validity of UQL. Please avoid composing statements that have no alias or defining alias that is not called later on.
Custom Alias
A custom alias is defined by developers using keyword as. The alias defined in the previous table (nodes, paths, name, birthday, edgeUUIDs and record) are all custom aliases.
Do not define the same alias for different values in a UQL statement. Avoid defining alias using the property names of nodes or edges, and system alias this may be used to disambiguate when necessary.
- 1 ~ 64 characters
- Not allow to start with wave line '~'
- Not allow to contain back quote '`'
- Not allow to use Reserved Words listed in Basic Concepts
- (When containing characters other than letters, numbers and underscore, the alias name should be wrapped with backquote '`' when being used in the UQL)
A custom alias may represent: NODE, EDGE, PATH, ATTR, ARRAY, TABLE
Life cycle of a customer alias: anywhere after the alias is defined.
System Alias
System alias are defined by Ultipa system. They can be used directly without definition:
System Alias |
Meaning | Data Structure |
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 basic template |
prev_e |
The previous edge of the current node or edge | EDGE | In the filter of any basic template |
Please read chapter Path | SubGraph | Template - prev_n and Path | SubGraph | Template - prev_efor details on prev_n and prev_e.
In practical this is rarely used unless to eliminate any ambiguity; ambiguity occurs when the property names of the node/edge correspond with the custom alias, in which case this has to be used to refer to the property of node/edge.
... as balance
find().nodes({this.balance > 5000})
Note: this.balance in nodes() represents the property balance of the current node; since the custom alias defined in the previous statement is 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
Suppose that nodes, edges, paths, attr, array and table are aliases of NODE, EDGE, PATH, ATTR, ARRAY and TABLE, below call formats are supported:
| Call Format | Result |
Specification | Content |
|---|---|---|---|
nodes.<property> |
ATTR | Call in any statement | Node property (or null if the node property does not exist) |
nodes.@ |
ATTR | Call in any statement | Node schema |
nodes |
NODE | Call in any statement | Node data structure without any custom properties |
nodes{<property>, ...} |
NODE | Call in RETURN clause | Node data structure with designated custom properties |
nodes{*} |
NODE | Call in RETURN clause | Node data structure with all custom properties |
edges.<property> |
ATTR | Call in any statement | Edge property (or null if the edge property does not exist) |
edges.@ |
ATTR | Call in any statement | Edge schema |
edges |
EDGE | Call in any statement | Edge data structure without any custom properties |
edges{<property>, ...} |
EDGE | Call in RETURN clause | Edge data structure with designated custom properties |
edges{*} |
EDGE | Call in RETURN clause | Edge data structure with all custom properties |
paths |
PATH | Call in any statement | Path data structure without any custom properties of its nodes and edges |
paths{<property>, ...}{<property>, ...} |
PATH | Call in RETURN clause | Path data structure with designated custom properties of its nodes and designated custom properties of its edges |
paths{*}{<property>, ...} |
PATH | Call in RETURN clause | Path data structure with all custom properties of its nodes and designated custom properties of its edges |
paths{<property>, ...}{*} |
PATH | Call in RETURN clause | Path data structure with designated custom properties of its nodes and all custom properties of its edges |
paths{<property>} |
PATH | Call in RETURN clause | Path data structure with designated custom properties of its nodes and edges |
paths{*} |
PATH | Call in RETURN clause | Path data structure with all custom properties of its nodes and edges |
attr |
ATTR | Call in any statement | The atomic value |
array |
ARRAY | Call in any statement | The array |
array[n] |
ATTR | Call in any statement | The element of array with index n |
array[n1:n2] |
ARRAY | Call in any statement | A sub-array formed by element with index n1~n2 |
array[:n] |
ARRAY | Call in any statement | A sub-array formed by element with index 0~n |
array[n:] |
ARRAY | Call in any statement | A sub-array formed by element with index n~<length-1> |
table |
TABLE | Call in RETURN clause | The table |
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.
Read chapter Data Stream | Clause for the detailed description of RETURN.