Transactions With Deletion
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class Database | |
def initialize | |
@count_versions = [Hash.new(0)] | |
@db_versions = [Hash.new()] | |
@deletion_keys = [[]] | |
@tier = 0 | |
end | |
# CRUD COMMANDS | |
def set(key, value) | |
@db_versions[@tier][key] = value | |
@count_versions[@tier][value] += 1 | |
return nil | |
end | |
def get(key) | |
merge_candidate.fetch(key, "NULL") | |
end | |
def count(value) | |
count_candidate.fetch(value, 0) | |
end | |
def delete(key) | |
value = merge_candidate[key] | |
if value | |
@deletion_keys[@tier].push(key) | |
@db_versions[@tier].delete(key) | |
@count_versions[@tier][value] -= 1 | |
return nil | |
else | |
return "That key isn't in the database!" | |
end | |
end | |
#TRANSACTION MANAGEMENT | |
def begin() | |
@db_versions.push(Hash.new()) | |
@count_versions.push(Hash.new(0)) | |
@deletion_keys.push([]) | |
@tier += 1 | |
return nil | |
end | |
def rollback() | |
if @tier == 0 | |
return "No transaction in progress" | |
end | |
@db_versions.pop | |
@count_versions.pop | |
@deletion_keys.pop | |
@tier -= 1 | |
return nil | |
end | |
def commit() | |
if @tier == 0 | |
return "No transaction in progress" | |
end | |
@db_versions[-2] = merge_candidate(@tier, @tier-1, @db_versions[0]) | |
@deletion_keys[-1].each{|key| @db_versions[-2].delete(key)} | |
@count_versions[-2] = count_candidate(@tier, @tier-1, @count_versions[0]) | |
@db_versions.pop | |
@count_versions.pop | |
@deletion_keys.pop | |
@tier -= 1 | |
return nil | |
end | |
private | |
def merge_candidate(start_tier=@tier, end_tier=0, merge_item=@db_versions[end_tier]) | |
if start_tier == end_tier | |
@deletion_keys[-1].each{|key| merge_item.delete(key)} if @deletion_keys[-1] | |
return merge_item | |
else | |
step = @db_versions[start_tier].merge(merge_item) { |key, canonical_value, transactional_value| | |
transactional_value || canonical_value | |
} | |
return merge_candidate start_tier-1, end_tier,step | |
end | |
end | |
def count_candidate(start_tier=@tier, end_tier=0, merge_item=@count_versions[0]) | |
if start_tier == end_tier | |
return merge_item | |
else | |
step = @count_versions[start_tier].merge(merge_item) { |key, canonical_value, transactional_value| | |
canonical_value + transactional_value | |
} | |
return count_candidate start_tier-1, end_tier,step | |
end | |
end | |
end |
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