在某些情况下,如果同一表有多个联接,则ActiveRecord设置别名表名称。我陷入了这些联接包含范围(使用“合并”)的情况。
我有多对多关系:
型号table_name:
users
第二个模型table_name:
posts
联接表名称:
access_levels
帖子通过access_levels具有许多用户,反之亦然。
用户模型和发布模型两者共享相同的关系:
has_many :access_levels, -> { merge(AccessLevel.valid) }
AccessLevel模型内部的范围如下所示:
# v1
scope :valid, -> {
where("(valid_from IS NULL OR valid_from < :now) AND (valid_until IS NULL OR valid_until > :now)", :now => Time.zone.now)
}
# v2
# scope :valid, -> {
# where("(#{table_name}.valid_from IS NULL OR #{table_name}.valid_from < :now) AND (#{table_name}.valid_until IS NULL OR #{table_name}.valid_until > :now)", :now => Time.zone.now)
# }
我想这样称呼某事:
Post.joins(:access_levels).joins(:users).where (...)
ActiveRecord为第二个连接创建别名(“ access_levels_users”)。我想在AccessLevel模型的“有效”范围内引用此表名。
V1显然会生成PG::AmbiguousColumn
-Error。V2会在两个条件前加上access_levels.
,这在语义上是错误的。
这就是我生成查询的方式:(简体)
# inside of a policy
scope = Post.
joins(:access_levels).
where("access_levels.level" => 1, "access_levels.user_id" => current_user.id)
# inside of my controller
scope.joins(:users).select([
Post.arel_table[Arel.star],
"hstore(array_agg(users.id::text), array_agg(users.email::text)) user_names"
]).distinct.group("posts.id")
生成的查询如下所示(使用valid
上面的范围v2):
SELECT "posts".*, hstore(array_agg(users.id::text), array_agg(users.email::text)) user_names
FROM "posts"
INNER JOIN "access_levels" ON "access_levels"."post_id" = "posts"."id" AND (("access_levels"."valid_from" IS NULL OR "access_levels"."valid_from" < '2014-07-24 05:38:09.274104') AND ("access_levels"."valid_until" IS NULL OR "access_levels"."valid_until" > '2014-07-24 05:38:09.274132'))
INNER JOIN "users" ON "users"."id" = "access_levels"."user_id"
INNER JOIN "access_levels" "access_levels_posts" ON "access_levels_posts"."post_id" = "posts"."id" AND (("access_levels"."valid_from" IS NULL OR "access_levels"."valid_from" < '2014-07-24 05:38:09.274675') AND ("access_levels"."valid_until" IS NULL OR "access_levels"."valid_until" > '2014-07-24 05:38:09.274688'))
WHERE "posts"."deleted_at" IS NULL AND "access_levels"."level" = 4 AND "access_levels"."user_id" = 1 GROUP BY posts.id
ActiveRecord为access_levels表的第二个联接设置适当的别名“ access_levels_posts”。问题是合并的valid
-scope在列的前面加上“ access_levels”而不是“ access_levels_posts”。我还尝试使用arel生成范围:
# v3
scope :valid, -> {
where arel_table[:valid_from].eq(nil).or(arel_table[:valid_from].lt(Time.zone.now)).and(
arel_table[:valid_until].eq(nil).or(arel_table[:valid_until].gt(Time.zone.now))
)
}
结果查询保持不变。
同时,我已经能够解决自己的问题。我将发布解决方案以帮助遇到类似问题的其他人。
序言:通往应许之地的路很长;)
我将使设置尽可能短:
#
# Setup
#
class Post < ActiveRecord::Base
has_many :access_levels, -> { merge(AccessLevel.valid) }
has_many :users, :through => :access_levels
end
class AccessLevel < ActiveRecord::Base
belongs_to :post
belongs_to :user
scope :valid, -> {
where arel_table[:valid_from].eq(nil).or(arel_table[:valid_from].lt(Time.zone.now)).and(
arel_table[:valid_until].eq(nil).or(arel_table[:valid_until].gt(Time.zone.now))
)
}
enum :level => [:publisher, :subscriber]
end
class User < ActiveRecord::Base
has_many :access_levels, -> { merge(AccessLevel.valid) }
has_many :users, :through => :access_levels
end
最初的目标是调用这样的名称(以添加更多条件等):
Post.joins(:users).joins(:access_levels)
这导致语义错误的查询:
SELECT "posts".* FROM "posts"
INNER JOIN "access_levels"
ON "access_levels"."post_id" = "posts"."id"
AND (("access_levels"."valid_from" IS NULL OR "access_levels"."valid_from" < '2014-09-15 20:42:46.835548')
AND ("access_levels"."valid_until" IS NULL OR "access_levels"."valid_until" > '2014-09-15 20:42:46.835688'))
INNER JOIN "users"
ON "users"."id" = "access_levels"."user_id"
INNER JOIN "access_levels" "access_levels_posts"
ON "access_levels_posts"."post_id" = "posts"."id"
AND (("access_levels"."valid_from" IS NULL OR "access_levels"."valid_from" < '2014-09-15 20:42:46.836090')
AND ("access_levels"."valid_until" IS NULL OR "access_levels"."valid_until" > '2014-09-15 20:42:46.836163'))
第二个联接使用别名-但条件不是使用该别名。
救急!
我已经使用裸露的竞技场建立了以下所有联接,而不是信任ActiveRecord。不幸的是,似乎两者都不总是能按预期进行。但是至少它一直都在工作。我在此示例中使用外部联接,因此无论如何我都必须自己构建它们。此外,所有这些查询都存储在策略内部(使用Pundit)。因此它们很容易测试,并且没有胖控制器或任何冗余。所以我可以添加一些额外的代码。
#
# Our starting point ;)
#
scope = Post
#
# Rebuild `scope.joins(:users)` or `scope.joins(:access_levels => :user)`
# No magic here.
#
join = Post.arel_table.join(AccessLevel.arel_table, Arel::Nodes::OuterJoin).on(
Post.arel_table[:id].eq(AccessLevel.arel_table[:post_id]).
and(AccessLevel.valid.where_values)
).join_sources
scope = scope.joins(join)
join = AccessLevel.arel_table.join(User.arel_table, Arel::Nodes::OuterJoin).on(
AccessLevel.arel_table[:user_id].eq(User.arel_table[:id])
).join_sources
scope = scope.joins(join)
#
# Now let's join the access_levels table for a second time while reusing the AccessLevel.valid scope.
# To accomplish that, we temporarily swap AccessLevel.table_name
#
table_alias = 'al' # This will be the alias
temporary_table_name = AccessLevel.table_name # We want to restore the original table_name later
AccessLevel.table_name = table_alias # Set the alias as the table_name
valid_clause = AccessLevel.valid.where_values # Store the condition with our temporarily table_name
AccessLevel.table_name = temporary_table_name # Restore the original table_name
#
# We're now able to use the table_alias combined with our valid_clause
#
join = Post.arel_table.join(AccessLevel.arel_table.alias(table_alias), Arel::Nodes::OuterJoin).on(
Post.arel_table[:id].eq(AccessLevel.arel_table.alias(table_alias)[:post_id]).
and(valid_clause)
).join_sources
scope = scope.joins(join)
经过所有的血汗和眼泪,这是我们的结果查询:
SELECT "posts".* FROM "posts"
LEFT OUTER JOIN "access_levels"
ON "posts"."id" = "access_levels"."post_id"
AND ("access_levels"."valid_from" IS NULL OR "access_levels"."valid_from" < '2014-09-15 20:35:34.420077')
AND ("access_levels"."valid_until" IS NULL OR "access_levels"."valid_until" > '2014-09-15 20:35:34.420189')
LEFT OUTER JOIN "users"
ON "access_levels"."user_id" = "users"."id"
LEFT OUTER JOIN "access_levels" "al"
ON "posts"."id" = "al"."post_id"
AND ("al"."valid_from" IS NULL OR "al"."valid_from" < '2014-09-15 20:35:41.678492')
AND ("al"."valid_until" IS NULL OR "al"."valid_until" > '2014-09-15 20:35:41.678603')
现在所有条件都使用适当的别名!
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