Class: Sequel::Postgres::PropertyGraph::Table

Inherits:
Object
  • Object
show all
Includes:
SQL::AliasMethods
Defined in:
lib/sequel/adapters/shared/postgres.rb

Overview

Represents a GRAPH_TABLE expression, used to query a property graph via graph pattern matching. This is used in place of a table name expression or dataset in a SELECT query. These are created by calling #graph_table on the related Database object.

Table uses a method chaining design, similar to Dataset, where methods return modified frozen copies of the object.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from SQL::AliasMethods

#as

Constructor Details

#initialize(name, elements, columns) ⇒ Table

Returns a new instance of Table.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 687

def initialize(name, elements, columns)
  @name = name
  @elements = elements
  @columns = columns
  freeze
end

Instance Attribute Details

#columns(*cols) ⇒ Object (readonly)

Return a modifies copy that uses the given columns. A graph table must have a least one column set before it is used in a query.

DB.graph_table(:gn, :v).columns(:a, Sequel[:b].as(:c))
# GRAPH_TABLE (gn MATCH (IS v) COLUMNS (a, b AS c))


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# File 'lib/sequel/adapters/shared/postgres.rb', line 676

def columns
  @columns
end

#elements ⇒ Object (readonly)

A frozen array of Element instances, representing the vertices and edges in the graph pattern.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 672

def elements
  @elements
end

#name ⇒ Object (readonly)

The name of the property graph the table is querying.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 668

def name
  @name
end

Class Method Details

.create(graph_name, initial_vertex_label, initial_vertex_opts) ⇒ Object

Create a new Table with the given graph_name, with initial_vertex_label and initial_vertex_opts being used to create the initial vertex. See Table#link for which options are supported for the initial vertex.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 682

def self.create(graph_name, initial_vertex_label, initial_vertex_opts)
  vertex = Element.create(:vertex, "", initial_vertex_label, initial_vertex_opts)
  new(graph_name, [vertex].freeze, [].freeze)
end

Instance Method Details

#add_columns(*cols) ⇒ Object

Return a modified copy that adds the given columns to the existing list of columns for the graph table.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 745

def add_columns(*cols)
  columns(*@columns, *cols)
end

#columns_used ⇒ Object

A frozen array of the columns used in the COLUMNS clause (aliased as columns_used, as #columns is used to modify the columns).



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# File 'lib/sequel/adapters/shared/postgres.rb', line 677

def columns
  @columns
end

#from(label, opts = OPTS) ⇒ Object

Similar to #link, but uses a directed link from the new element to the previous element (<- in the graph pattern). Accepts same arguments and options as #link.

DB.graph_table(:gn, :v).from(:e)
# GRAPH_TABLE (gn MATCH (IS v)<-[IS e])


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# File 'lib/sequel/adapters/shared/postgres.rb', line 730

def from(label, opts=OPTS)
  append_element('<-', label, opts)
end

#link(label, opts = OPTS) ⇒ Object

Return a modified copy with an element added using a bidirectional link (- in the graph pattern). label specifies the label restriction for the element. This can be nil for no label restriction, or an array or set to restrict to the given labels.

Options supported: :var :: Specifies a graph pattern variable name for the element, usable in the WHERE or COLUMNS clauses. :vertex :: Specifies that the element being linked to is a vertex. This allows for direct vertex<->vertex linking, instead of the default vertex<->edge<->vertex linking. :where :: An expression to use for the WHERE clause for the element.

DB.graph_table(:gn, :v).link(:e)
# GRAPH_TABLE (gn MATCH (IS v)-[IS e])


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# File 'lib/sequel/adapters/shared/postgres.rb', line 710

def link(label, opts=OPTS)
  append_element('-', label, opts)
end

#sql_literal_append(ds, sql) ⇒ Object

Append the SQL for the GRAPH_TABLE expression to the given SQL string. Requires graph table have at least one column set.



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# File 'lib/sequel/adapters/shared/postgres.rb', line 751

def sql_literal_append(ds, sql)
  if @columns.empty?
    raise Error, "cannot use graph_table in a query if it does not return any columns"
  end
  if @elements.last.type == :edge
    raise Error, "cannot use graph_table in a query if the last element is an edge"
  end

  sql << "GRAPH_TABLE ("
  ds.literal_append(sql, @name)
  sql << " MATCH "

  @elements.each do |element|
    marker = element.marker
    var = element.var
    label = element.label
    where = element.where
    vertex = element.type == :vertex

    sql << marker
    sql << (vertex ? '(' : '[')

    ds.literal_append(sql, var) if var
    if label 
      sql << (var ? " IS " : "IS ")
      if label.is_a?(Array)
        label_sep = ""
        label.each do |l|
          sql << label_sep
          label_sep = "|" if label_sep.empty?
          ds.literal_append(sql, l)
        end
      else
        ds.literal_append(sql, label)
      end
    end

    if where
      sql << ((var || label) ? " WHERE " : "WHERE ")
      ds.literal_append(sql, where)
    end

    sql << (vertex ? ')' : ']')
  end

  sql << " COLUMNS "
  ds.literal_append(sql, @columns)
  sql << ")"
end

#to(label, opts = OPTS) ⇒ Object

Similar to #link, but uses a directed link from the previous element to the new element (-> in the graph pattern). Accepts same arguments and options as #link.

DB.graph_table(:gn, :v).to(:e)
# GRAPH_TABLE (gn MATCH (IS v)->[IS e])


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# File 'lib/sequel/adapters/shared/postgres.rb', line 720

def to(label, opts=OPTS)
  append_element('->', label, opts)
end