Problem parsing oC_MultiPartQuery with ANTLR4

[dahoat]

Hi to all,

I am using the ANTLR4 grammar in version M16 (https://s3.amazonaws.com/artifacts.opencypher.org/M16/Cypher.g4) and have an issue with oC_MultiPartQuery:

In the grammar, it says:

oC_MultiPartQuery
              :  ( ( oC_ReadingClause SP? )* ( oC_UpdatingClause SP? )* oC_With SP? )+ oC_SinglePartQuery ;

To my understanding, it is therefore possible to write something like this

MATCH (c:Label), (d:Label2) SET c.property = d.property WITH c MATCH (e:Label3 {name: c.name}) RETURN c

However, in the ANTLR4 parser (Java), i only get List<oC_ReadingClause>, List<oC_UpdatingClause> and List<oC_With>. Therefore, I cannot distinguish whether (e:Label3 {name: c.name}) belongs before which entry in List<oC_With> or after any entry.

Therfore, I propose changing the grammar to something like

oC_MultiPartQuery
              :  ( oC_MultiPartQueryGroup )+ oC_SinglePartQuery ;

oC_MultiPartQueryGroup
              :  ( oC_ReadingClause SP? )* ( oC_UpdatingClause SP? )* oC_With SP? ;

I am no expert in grammars so please excuse me if I missed something here.

All the best,
Daniel

[hvub]

Hi Daniel,

thanks for your question and for using the openCypher artifacts.

I understand, you have some trouble consuming the parsing result from Antlr. I am not an Antlr expert by any means. According to my thin understanding, the parser gives you a parse tree back, which contains all the necessary information. The tree knows the order in which the grammar rules have parse which parts of the input. This information clear allows to decide to which MATCH clause a pattern belongs and if that MATCH clause appears before or after a WITH clause.

A sample output of the parse tree for your query looks like this:

  oC_Cypher
    oC_Statement
      oC_Query
        oC_RegularQuery
          oC_SingleQuery
            oC_MultiPartQuery
              oC_ReadingClause
                oC_Match
                  "MATCH"
                  " "
                  oC_Pattern
                    oC_PatternPart
                      oC_AnonymousPatternPart
                        oC_PatternElement
                          oC_NodePattern
                            "("
                            oC_Variable
                              oC_SymbolicName
                                "c"
                            oC_NodeLabels
                              oC_NodeLabel
                                ":"
                                oC_LabelName
                                  oC_SchemaName
                                    oC_SymbolicName
                                      "Label"
                            ")"
                    ","
                    " "
                    oC_PatternPart
                      oC_AnonymousPatternPart
                        oC_PatternElement
                          oC_NodePattern
                            "("
                            oC_Variable
                              oC_SymbolicName
                                "d"
                            oC_NodeLabels
                              oC_NodeLabel
                                ":"
                                oC_LabelName
                                  oC_SchemaName
                                    oC_SymbolicName
                                      "Label2"
                            ")"
              " "
              oC_UpdatingClause
                oC_Set
                  "SET"
                  " "
                  oC_SetItem
                    oC_PropertyExpression
                      oC_Atom
                        oC_Variable
                          oC_SymbolicName
                            "c"
                      oC_PropertyLookup
                        "."
                        oC_PropertyKeyName
                          oC_SchemaName
                            oC_SymbolicName
                              "property"
                    " "
                    "="
                    " "
                    oC_Expression
                      oC_OrExpression
                        oC_XorExpression
                          oC_AndExpression
                            oC_NotExpression
                              oC_ComparisonExpression
                                oC_AddOrSubtractExpression
                                  oC_MultiplyDivideModuloExpression
                                    oC_PowerOfExpression
                                      oC_UnaryAddOrSubtractExpression
                                        oC_StringListNullOperatorExpression
                                          oC_PropertyOrLabelsExpression
                                            oC_Atom
                                              oC_Variable
                                                oC_SymbolicName
                                                  "d"
                                            oC_PropertyLookup
                                              "."
                                              oC_PropertyKeyName
                                                oC_SchemaName
                                                  oC_SymbolicName
                                                    "property"
              " "
              oC_With
                "WITH"
                oC_ProjectionBody
                  " "
                  oC_ProjectionItems
                    oC_ProjectionItem
                      oC_Expression
                        oC_OrExpression
                          oC_XorExpression
                            oC_AndExpression
                              oC_NotExpression
                                oC_ComparisonExpression
                                  oC_AddOrSubtractExpression
                                    oC_MultiplyDivideModuloExpression
                                      oC_PowerOfExpression
                                        oC_UnaryAddOrSubtractExpression
                                          oC_StringListNullOperatorExpression
                                            oC_PropertyOrLabelsExpression
                                              oC_Atom
                                                oC_Variable
                                                  oC_SymbolicName
                                                    "c"
              " "
              oC_SinglePartQuery
                oC_ReadingClause
                  oC_Match
                    "MATCH"
                    " "
                    oC_Pattern
                      oC_PatternPart
                        oC_AnonymousPatternPart
                          oC_PatternElement
                            oC_NodePattern
                              "("
                              oC_Variable
                                oC_SymbolicName
                                  "e"
                              oC_NodeLabels
                                oC_NodeLabel
                                  ":"
                                  oC_LabelName
                                    oC_SchemaName
                                      oC_SymbolicName
                                        "Label3"
                              " "
                              oC_Properties
                                oC_MapLiteral
                                  "{"
                                  oC_PropertyKeyName
                                    oC_SchemaName
                                      oC_SymbolicName
                                        "name"
                                  ":"
                                  " "
                                  oC_Expression
                                    oC_OrExpression
                                      oC_XorExpression
                                        oC_AndExpression
                                          oC_NotExpression
                                            oC_ComparisonExpression
                                              oC_AddOrSubtractExpression
                                                oC_MultiplyDivideModuloExpression
                                                  oC_PowerOfExpression
                                                    oC_UnaryAddOrSubtractExpression
                                                      oC_StringListNullOperatorExpression
                                                        oC_PropertyOrLabelsExpression
                                                          oC_Atom
                                                            oC_Variable
                                                              oC_SymbolicName
                                                                "c"
                                                          oC_PropertyLookup
                                                            "."
                                                            oC_PropertyKeyName
                                                              oC_SchemaName
                                                                oC_SymbolicName
                                                                  "name"
                                  "}"
                              ")"
                " "
                oC_Return
                  "RETURN"
                  oC_ProjectionBody
                    " "
                    oC_ProjectionItems
                      oC_ProjectionItem
                        oC_Expression
                          oC_OrExpression
                            oC_XorExpression
                              oC_AndExpression
                                oC_NotExpression
                                  oC_ComparisonExpression
                                    oC_AddOrSubtractExpression
                                      oC_MultiplyDivideModuloExpression
                                        oC_PowerOfExpression
                                          oC_UnaryAddOrSubtractExpression
                                            oC_StringListNullOperatorExpression
                                              oC_PropertyOrLabelsExpression
                                                oC_Atom
                                                  oC_Variable
                                                    oC_SymbolicName
                                                      "c"
    "<EOF>"

I have written some demo code for how to use the Antlr parser (which produced the above output). See PR #518.

There are two ways to consume the parse tree: Either with a tree listener or by manually walking the tree structure. I guess, the first is preferable.

There are two ways get the parser: Either you build directly from the g4 grammar published on the oC webpage or you create the parser from the grammar xml files in this repository (which generate the g4 grammar as an intermediate step). I guess, the first is preferable.

The demo shows all four possible combination of these options.

[dahoat]

Hi hvub,

I am very sorry, I obviously messed up the example. Therefore, I created repository https://github.com/dahoat/OpenCypherExperiments with an running example (Maven/Spring). I also have to mention, I am using Visitors instead of Listeners.

The query

MATCH (a) WITH a MATCH (b) SET a.prop = 'match 2' WITH a, b MATCH (c) WITH a, b, c MATCH (d) RETURN *

is a much better example to my problem.

All the best,
Daniel

[hvub]

Hi Daniel,

I have modified your visitor here
dahoat/OpenCypherExperiments#1
to demonstrate how you can reproduce the groups without needing a grammar changes.

Hope it helps.
-H