重構可選參數刪除`if`語句的方法

Question

我有一個方法select_active_buildings有三個參數，默認爲nil來使用提供的信息過濾我的數據庫。

def select_active_buildings(category:nil, upgrader:nil, upgrade_resource:nil) 
    my_active_buildings = self.buildings.active(self.townhall_level) 
    if category && upgrader && upgrade_resource 
    return my_active_buildings.where(category:category, upgrader:upgrader, upgrade_resource:upgrade_resource) 
    elsif category && upgrader 
    return my_active_buildings.where(category:category, upgrader:upgrader) 
    elsif category && upgrade_resource 
    return my_active_buildings.where(category:category, upgrade_resource:upgrade_resource) 
    elsif upgrader && upgrade_resource 
    return my_active_buildings.where(upgrader:upgrader, upgrade_resource:upgrade_resource) 
    elsif category 
    return my_active_buildings.where(category:category) 
    elsif upgrader 
    return my_active_buildings.where(upgrader:upgrader) 
    elsif upgrade_resource 
    return my_active_buildings.where(upgrade_resource:upgrade_resource) 
    else 
    return my_active_buildings 
    end 
end 

我需要幫助重構此方法。

Answer 1

假設你用ActiveRecord，Mongoid，或用可鏈接where做別的事情，你可以採取的事實，即這樣的：

o.where(:a => b, :c => d) 

是一樣的：

o.where(:a => b).where(:c => d) 

這可以讓你做到這一點：

def select_active_buildings(category: nil, upgrader: nil, upgrade_resource: nil) 
    buildings = self.buildings.active(self.townhall_level) 
    buildings = buildings.where(category: category) if(category) 
    buildings = buildings.where(upgrader: upgrader) if(upgrader) 
    buildings = buildings.where(upgrade_resource: upgrade_resource) if(upgrade_resource) 
    buildings 
end 

甚至：

def select_active_buildings(conditions) 
    buildings = self.buildings.active(self.townhall_level) 
    %i[category upgrader upgrade_resource] 
    .select { |f| conditions.has_key?(f) } 
    .inject(buildings) { |q, f| q.where(f => conditions[f]) } 
end 

Answer 2

我應該這樣做：

def select_active_buildings(category: nil, upgrader: nil, upgrade_resource: nil) 
    my_active_buildings = self.buildings.active(self.townhall_level) 
    cond = { 
    category: category, 
    upgrader: upgrader, 
    upgrade_resource: upgrade_resource 
    }.select { |k, v| v } 
    my_active_buildings.where(cond) 
end 

或者，

def select_active_buildings(category: nil, upgrader: nil, upgrade_resource: nil) 
    my_active_buildings = self.buildings.active(self.townhall_level) 
    cond = {} 
    cond[:category] = category if category 
    cond[:upgrader] = upgrader if upgrader 
    cond[:upgrade_resource] = upgrade_resource if upgrade_resource 
    my_active_buildings.where(cond) 
end 

或者，如果我真的不關心語法在select_active_function水平檢查，

def select_active_buildings(cond) 
    my_active_buildings = self.buildings.active(self.townhall_level) 
    my_active_buildings.where(cond) 
end 

如果你真的不想要.where({})的情況下，你可以把它放在return my_active_buildings if cond.empty?之前。

Answer 3

def select_active_buildings(category: nil, upgrader: nil, upgrade_resource: nil) 
    buildings.active(self.townhall_level).where(
    **({category: category} if category).to_h, 
    **({upgrader: upgrader} if upgrader).to_h, 
    **({upgrade_resource: upgrade_resource} if upgrade_resource).to_h, 
) 
end