Class: ActiveRDF::Query

Inherits:
Object
  • Object
show all
Defined in:
lib/active_rdf/queryengine/query.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(resource_type = RDFS::Resource) ⇒ Query

Creates a new query. You may pass a different class that is used for “resource” type objects instead of RDFS::Resource



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# File 'lib/active_rdf/queryengine/query.rb', line 16

def initialize(resource_type = RDFS::Resource)
  @distinct = false
  @select_clauses = []
  @where_clauses = []
  @filter_clauses = {}
  @sort_clauses = []
  @limits = nil
  @offsets = nil
  @keywords = {}
  @reasoning = nil
  @all_types = false
  @nil_clause_idx = -1
  set_resource_class(resource_type)
end

Instance Attribute Details

#filter_clauses ⇒ Object (readonly)

Returns the value of attribute filter_clauses.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def filter_clauses
  @filter_clauses
end

#keywords ⇒ Object (readonly)

Returns the value of attribute keywords.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def keywords
  @keywords
end

#limits ⇒ Object (readonly)

Returns the value of attribute limits.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def limits
  @limits
end

#offsets ⇒ Object (readonly)

Returns the value of attribute offsets.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def offsets
  @offsets
end

#select_clauses ⇒ Object (readonly)

Returns the value of attribute select_clauses.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def select_clauses
  @select_clauses
end

#sort_clauses ⇒ Object (readonly)

Returns the value of attribute sort_clauses.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def sort_clauses
  @sort_clauses
end

#where_clauses ⇒ Object (readonly)

Returns the value of attribute where_clauses.



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# File 'lib/active_rdf/queryengine/query.rb', line 10

def where_clauses
  @where_clauses
end

Instance Method Details

#all_types(enabled = true) ⇒ Object

Set query to ignore language & datatypes for objects



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# File 'lib/active_rdf/queryengine/query.rb', line 96

def all_types(enabled = true)
  @all_types = enabled
  self
end

#ask ⇒ Object

Adds variables to ask clause (see SPARQL specification)



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# File 'lib/active_rdf/queryengine/query.rb', line 76

def ask
  @ask = true
  self
end

#clear_select ⇒ Object

Clears the select clauses



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# File 'lib/active_rdf/queryengine/query.rb', line 60

def clear_select
  ActiveRdfLogger::log_debug "Cleared select clause", self
  @select_clauses = []
  @distinct = false
end

#count(*s) ⇒ Object

Adds variables to count clause



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# File 'lib/active_rdf/queryengine/query.rb', line 109

def count *s
  @count = true
  select(*s)
end

#datatype(variable, type) ⇒ Object 



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# File 'lib/active_rdf/queryengine/query.rb', line 160

def datatype(variable, type)
  filter(variable,:datatype,type)
end

#distinct(*s) ⇒ Object Also known as: select_distinct

Adds variables to select distinct clause



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# File 'lib/active_rdf/queryengine/query.rb', line 102

def distinct *s
  @distinct = true
  select(*s)
end

#execute(options = {:flatten => false}, &block) ⇒ Object

Executes query on data sources. Either returns result as array (flattened into single value unless specified otherwise) or executes a block (number of block variables should be same as number of select variables)

usage

results = query.execute

usage

query.execute do |s,p,o| … end



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# File 'lib/active_rdf/queryengine/query.rb', line 226

def execute(options={:flatten => false}, &block)
  options = {:flatten => true} if options == :flatten

  prepared_query = prepare_query(options)

  if block_given?
    for result in FederationManager.execute(prepared_query, options.merge(:flatten => false))
      yield result
    end
  else
    FederationManager.execute(prepared_query, options)
  end
end

#filter(variable, operator, operand) ⇒ Object

adds operator filter on one variable variable is a Ruby symbol that appears in select/where clause, operator is a SPARQL operator (e.g. ‘>’,‘lang’,‘datatype’), operand is a SPARQL value (e.g. 15)

Raises:



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# File 'lib/active_rdf/queryengine/query.rb', line 136

def filter(variable, operator, operand)
  raise(ActiveRdfError, "variable must be a Symbol") unless variable.is_a? Symbol
  @filter_clauses[variable] = [operator.to_sym,operand]
  self
end

#initialize_copy(orig) ⇒ Object 



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# File 'lib/active_rdf/queryengine/query.rb', line 48

def initialize_copy(orig)
  # dup the instance variables so we're not messing with the original query's values
  instance_variables.each do |iv|
    orig_val = instance_variable_get(iv)
    case orig_val
    when Array,Hash
      instance_variable_set(iv,orig_val.dup)
    end
  end
end

#keyword_where(s, o) ⇒ Object

Adds keyword constraint to the query. You can use all Ferret query syntax in the constraint (e.g. keyword_where(:s,‘eyal|benjamin’)



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# File 'lib/active_rdf/queryengine/query.rb', line 209

def keyword_where s,o
  @keyword = true
  if @keywords.include?(s)
    @keywords[s] = @keywords[s] + ' ' + o
  else
    @keywords[s] = o
  end
  self
end

#lang(variable, tag, exact = true) ⇒ Object

filter variable on specified language tag, e.g. lang(:o, ‘en’, true) optionally matches exactly on language dialect, otherwise only language-specifier is considered



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# File 'lib/active_rdf/queryengine/query.rb', line 156

def lang(variable, tag, exact=true)
  filter(variable,:lang,[tag.sub(/^@/,''),exact])
end

#limit(i) ⇒ Object

Adds limit clause (maximum number of results to return)



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# File 'lib/active_rdf/queryengine/query.rb', line 165

def limit(i)
  @limits = i.to_i
  self
end

#offset(i) ⇒ Object

Add offset clause (ignore first n results)



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# File 'lib/active_rdf/queryengine/query.rb', line 171

def offset(i)
  @offsets = i.to_i
  self
end

#reasoning(bool) ⇒ Object

Request reasoning be performed on query



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# File 'lib/active_rdf/queryengine/query.rb', line 82

def reasoning(bool)
  @reasoning = truefalse(bool)
  self
end

#reasoning=(bool) ⇒ Object 



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# File 'lib/active_rdf/queryengine/query.rb', line 87

def reasoning=(bool)
  self.reasoning(bool)
end

#reasoning? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/active_rdf/queryengine/query.rb', line 91

def reasoning?
  @reasoning
end

#regexp(variable, regexp) ⇒ Object Also known as: regex

adds regular expression filter on one variable variable is Ruby symbol that appears in select/where clause, regex is Ruby regular expression

Raises:



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# File 'lib/active_rdf/queryengine/query.rb', line 145

def regexp(variable, regexp)
  raise(ActiveRdfError, "variable must be a symbol") unless variable.is_a? Symbol
  regexp = regexp.source if(regexp.is_a?(Regexp))

  filter(variable, :regexp, regexp)
end

#resource_class ⇒ Object

This returns the class that is be used for resources, by default this is RDFS::Resource



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# File 'lib/active_rdf/queryengine/query.rb', line 33

def resource_class
  @resource_class ||= RDFS::Resource
end

#reverse_sort(*s) ⇒ Object

adds reverse sorting predicates



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# File 'lib/active_rdf/queryengine/query.rb', line 125

def reverse_sort *s
  s.each do |var| 
    raise(ActiveRdfError, "variable must be a Symbol") unless var.is_a? Symbol
    @sort_clauses << [var,:desc]
  end
  self
end

#select(*s) ⇒ Object

Adds variables to select clause

Raises:



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# File 'lib/active_rdf/queryengine/query.rb', line 67

def select *s
  raise(ActiveRdfError, "variable must be a Symbol") unless s.all?{|var| var.is_a?(Symbol)}
  @select = true
  # removing duplicate select clauses
  @select_clauses.concat(s).uniq!
  self
end

#set_resource_class(resource_class) ⇒ Object

Sets the resource_class. Any class may be used, however it is required that it can be created using the uri of the resource as it’s only parameter and that it has an ‘uri’ property

Raises:

  • (ArgumentError) 


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# File 'lib/active_rdf/queryengine/query.rb', line 40

def set_resource_class(resource_class)
  raise(ArgumentError, "resource_class must be a class") unless(resource_class.class == Class)

  test = resource_class.new("http://uri")
  raise(ArgumentError, "Must have an uri property") unless(test.respond_to?(:uri))
  @resource_class = resource_class
end

#sort(*s) ⇒ Object

Adds sort predicates



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# File 'lib/active_rdf/queryengine/query.rb', line 116

def sort *s
  s.each do |var| 

    @sort_clauses << [var,:asc]
  end
  self
end

#to_s ⇒ Object

Returns query string depending on adapter (e.g. SPARQL, N3QL, etc.)



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# File 'lib/active_rdf/queryengine/query.rb', line 241

def to_s
  if ConnectionPool.read_adapters.empty?
    inspect
  else
    ConnectionPool.read_adapters.first.translate(prepare_query)
  end
end

#to_sp ⇒ Object

Returns SPARQL serialisation of query



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# File 'lib/active_rdf/queryengine/query.rb', line 250

def to_sp
  require 'queryengine/query2sparql' unless(defined?(Query2SPARQL))
  Query2SPARQL.translate(self)
end

#where(s, p, o, c = nil) ⇒ Object

Adds where clauses (s,p,o) where each constituent is either variable (:s) or an RDFS::Resource (or equivalent class). Keyword queries are specified with the special :keyword symbol: Query.new.select(:s).where(:s, :keyword, ‘eyal’)



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# File 'lib/active_rdf/queryengine/query.rb', line 179

def where s,p,o,c=nil
  case p
  when :keyword
    # treat keywords in where-clauses specially
    keyword_where(s,o)
  else
    # give nil clauses a unique variable
    s,p,o = [s,p,o].collect{|clause| clause.nil? ? "nil#{@nil_clause_idx += 1}".to_sym : clause}

    # remove duplicate variable bindings, e.g.
    # where(:s,type,:o).where(:s,type,:oo) we should remove the second clause,
    # since it doesn't add anything to the query and confuses the query
    # generator.
    # if you construct this query manually, you shouldn't! if your select
    # variable happens to be in one of the removed clauses: tough luck.
    unless (s.respond_to?(:uri) or s.is_a?(Symbol)) and (s.class != RDFS::BNode)
      raise(ActiveRdfError, "Cannot add a where clause with s #{s}: s must be a resource or a variable, is a #{s.class.name}")
    end
    unless (p.respond_to?(:uri) or p.is_a?(Symbol)) and (s.class != RDFS::BNode)
      raise(ActiveRdfError, "Cannot add a where clause with p #{p}: p must be a resource or a variable, is a #{p.class.name}")
    end
    raise(ActiveRdfErrror, "Cannot add a where clause where o is a blank node") if(o.class == RDFS::BNode)

    @where_clauses << [s,p,o,c]
  end
  self
end