Rails - 准备语句的构建条件数组

Question

I'm trying build a conditions array to be using in a prepared statement:

Cars.find(:all, :conditions=>["color = ? AND doors = ? AND type = ?", "black", "4", "sedan"])

I've tried doing the following but getting an error of "ActiveRecord::PreparedStatementInvalid (wrong number of bind variables (4 for 2)":

conditions = []
conditions += ["color = ?", "black"]
conditions += ["doors = ?", "4"]
conditions += ["type = ?", "sedan"]

Cars.find(:all, :conditions=>conditions)

What is the proper way of building a conditional for prepared statements?

Answer 1

The problem is that you are building a wrong query, since you pass the params to the questionmarks all the way through your statement.

Your resulting query looks something like this:

 => ["color = ?", "black", "doors = ?", "4", "type = ?", "sedan"] 

In order to achieve your desired array, you would have to do something like this.

conditions = []
conditions += ["color = ?", "black"]
array = ["doors = ?", "4"]
conditions[0].concat(" AND ")
conditions[0].concat(array[0])
conditions << array[1]

If you repeat the last steps, you should get your required result.

Answer 2

You might find this easier to do with a hash:

conditions = {}
conditions[:color] = "black"
conditions[:doors] = 4
conditions[:type] = "sedan"

Cars.find(:all, :conditions=>conditions)