Class: JSONArel::Resolver

Inherits:
Object
  • Object
show all
Defined in:
lib/json_arel.rb

Constant Summary collapse

VALID_OPERATORS = 
%w[$eq $not_eq $gt $gteq $lt $lteq $in]

Instance Method Summary collapse

Constructor Details

#initialize(tree) ⇒ Resolver

Returns a new instance of Resolver.



15
16
17
 
# File 'lib/json_arel.rb', line 15

def initialize(tree)
  @tree = tree
end

Instance Method Details

#parse_where(field, val) ⇒ Object 



76
77
78
79
80
81
82
83
84
85
86
87
88
89
 
# File 'lib/json_arel.rb', line 76

def parse_where(field, val)
  # TODO: Support OR
  # Return func, params.
  operator_index = field.index('$')
  if operator_index
    field, comparator = field[0..operator_index-1], field[operator_index..field.length]
    if !VALID_OPERATORS.include? comparator
      raise ResolverError, "#{comparator} is an invalid filter expression."
    end
  else
    comparator = '$eq'
  end
  return field, comparator[1..-1], val
end

#resolve ⇒ Object 



19
20
21
 
# File 'lib/json_arel.rb', line 19

def resolve
  resolve_node(@tree).to_sql
end

#resolve_node(node) ⇒ Object 



23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
 
# File 'lib/json_arel.rb', line 23

def resolve_node(node)

  # (with) SELECT (fields) FROM (from) (join) WHERE (CONDITIONS) (GROUPBY) (LIMIT)
  table = Arel::Table.new(node['from'])

  # Does it contain a CTE?
  ctes = (node['with'] || []).map do |cte|
    Arel::Nodes::As.new(Arel::Table.new(cte['as'].to_sym), resolve_node(cte['select']))
  end

  # Resolve the SELECT fields
  if node['fields'].class == String
    # Is it a single string we're selecting?
    node['fields'] = Arel.sql(node['fields'])
  elsif node['fields'].class == Array
    node['fields'] = node['fields'].map {|x| Arel.sql(x) }
  elsif node['fields'].class == Hash
    # Is it a hash?
    node['fields'] = node['fields'].map do |k,v|
      Arel.sql(k).as(v)
    end
  end

  # Resolve WHERE
  node['where'] = (node['where'] || {}).map do |key, val|
    field, comparator, value = parse_where(key, val)
    table[field.to_sym].send(comparator, val)
  end

  # Evaluate.
  table = table.where(node['where']) if node['where'].length > 0
  expr = table.project(node['fields'])

  # TODO: support JOIN

  # Resolve GROUP BY
  node['group'] ||= []
  if node['group'].class == String
    node['group'] = [node['group']]
  end
  node['group'] = node['group'].map {|x| Arel.sql(x) }
  expr = expr.group(node['group']) if node['group'].length > 0

  # Evaluate CTEs
  expr = expr.with(ctes) if ctes.length > 0

  # Resolve LIMIT / OFFSET
  expr.take(node['limit']) if node['limit']
  expr.skip(node['offset']) if node['offset']

  expr
end