如何判断DataMapper中是否存在表

Question

由于检查table_exists,此代码在最后一行失败了吗？如何在Datamapper中正确执行此操作？

require 'sinatra'
require 'DataMapper'

DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/blog.db")

class Post
    include DataMapper::Resource
    property :id, Serial
    property :title, String
    property :body, Text
    property :created_at, DateTime
end

DataMapper.finalize

# automatically create the post table
DataMapper.auto_migrate! unless Post.table_exists?

Answer 1

贾斯汀,

如果您有dm-migrations必需(这基本上意味着您仍在使用RDBMS适配器),您可以执行以下操作以查明是否存在表(或该表中的列).

# Find out if the table named 'people' exists
DataMapper.repository(:default).adapter.storage_exists?('people')

# Find out if there's a 'name' column in the 'people' table
DataMapper.repository(:default).adapter.field_exists?('people', 'name')

请注意,这些API方法只会混合到adapterif dm-migrations中,并且您使用的是DataObjectsAdapter后代.