英文:
Dynamic ConditionBuilder
问题
我的问题非常简单，我想动态创建过滤器并在查询输入中使用它。我必须明确指出，tf变量不能改变。
所以这是我做的：
totalFilter := expression.ConditionBuilder{}
filter := expression.Name("status").Equal(expression.Value("0"))
filter2 := expression.Name("foo").Equal(expression.Value("bar"))
filter3 := expression.Name("yes").Equal(expression.Value("no"))
tf := []expression.ConditionBuilder{filter, filter2, filter3}
for _, v := range tf {
totalFilter = totalFilter.And(v)
}
expr := expression.NewBuilder().WithFilter(totalFilter)
builder, err := expr.Build()
if err != nil {
log.Println(err)
return err
}
但问题是totalFilter是一个空结构体，所以它的mode变量等于0，然后引发警报，因为mode 0是unsetCond。
我找到的唯一解决方法是这样做：
for i, v := range tf {
if i == 0 {
totalFilter = v
} else {
totalFilter.And(v)
}
}
但我想知道是否还有其他解决方案。
英文:
My problem is pretty simple, I would like to dynamically create filters to use it in my query input.
I must precise that the tf variable can't change.
So here is what I did :
totalFilter := expression.ConditionBuilder{}filter := expression.Name("status").Equal(expression.Value("0"))filter2 := expression.Name("foo").Equal(expression.Value("bar"))filter3 := expression.Name("yes").Equal(expression.Value("no"))tf := []expression.ConditionBuilder{filter, filter2, filter3}for _, v := range tf {totalFilter = totalFilter.And(v)}expr := expression.NewBuilder().WithFilter(totalFilter)builder, err := expr.Build()if err != nil {log.Println(err)return err}
But the probleme is that totalFilter is an empty struct so it's mode variable is equal to 0 and then it raise an alert because mode 0 is unsetCond.
The only workaround that I found is to do this :
for i, v := range tf {if i == 0 {totalFilter = v} else {totalFilter.And(v)}}
But I was wondering if there is another solution.
答案1
得分: 1
你可以通过创建一个自定义的可变参数函数来抽象化对第一个expression.ConditionBuilder的处理，该函数至少需要一个expression.ConditionBuilder参数：
func And(first expression.ConditionBuilder, rest ...expression.ConditionBuilder) expression.ConditionBuilder {result := firstfor _, cb := range rest {result = result.And(cb)}return result}
然后，在main函数中使用：
filter := expression.Name("status").Equal(expression.Value("0"))filter2 := expression.Name("foo").Equal(expression.Value("bar"))filter3 := expression.Name("yes").Equal(expression.Value("no"))totalFilter := And(filter, filter2, filter3)expr := expression.NewBuilder().WithFilter(totalFilter)builder, err := expr.Build()// 其他操作...
请注意，expression包中还导出了一个名为And的类似函数，但它需要至少两个（而不仅仅是一个）expression.ConditionBuilder参数。这有点不幸...
英文:
You could abstract away the treatment of the first expression.ConditionBuilder in a custom variadic function taking at least one expression.ConditionBuilder parameter:
func And(first expression.ConditionBuilder, rest ...expression.ConditionBuilder) expression.ConditionBuilder {result := firstfor _, cb := range rest {result = result.And(cb)}return result}
Then, in main:
filter := expression.Name("status").Equal(expression.Value("0"))filter2 := expression.Name("foo").Equal(expression.Value("bar"))filter3 := expression.Name("yes").Equal(expression.Value("no"))totalFilter := And(filter, filter2, filter3)expr := expression.NewBuilder().WithFilter(totalFilter)builder, err := expr.Build()// etc.
Note that a similar function, also named And, is exported by the expression package, but it takes at least two (not just one) expression.ConditionBuilder parameters. That's unfortunate...
答案2
得分: 0
我的方法是创建一个“虚拟”条件，它始终返回true，就像动态SQL语句中常见的WHERE 1=1 [AND ...]条件一样。
示例代码将变为：
// 虚拟条件 (1=1) 用于初始化过滤器totalFilter := expression.Equal(expression.Value(1), expression.Value(1))filter := expression.Name("status").Equal(expression.Value("0"))filter2 := expression.Name("foo").Equal(expression.Value("bar"))filter3 := expression.Name("yes").Equal(expression.Value("no"))tf := []expression.ConditionBuilder{filter, filter2, filter3}for _, v := range tf {totalFilter = totalFilter.And(v)}expr := expression.NewBuilder().WithFilter(totalFilter)builder, err := expr.Build()if err != nil {log.Println(err)return err}
请注意，如果您的其他条件是通过“OR”操作连接的，则虚拟条件需要被反转，以便始终返回false。
英文:
My approach was to create a "dummy" condition that will always return true, much like the WHERE 1=1 [AND ...] condition that is common in dynamic SQL statements.
The example code would become:
// dummy condition (1=1) to initialize the filtertotalFilter := expression.Equal(expression.Value(1), expression.Value(1))filter := expression.Name("status").Equal(expression.Value("0"))filter2 := expression.Name("foo").Equal(expression.Value("bar"))filter3 := expression.Name("yes").Equal(expression.Value("no"))tf := []expression.ConditionBuilder{filter, filter2, filter3}for _, v := range tf {totalFilter = totalFilter.And(v)}expr := expression.NewBuilder().WithFilter(totalFilter)builder, err := expr.Build()if err != nil {log.Println(err)return err}
Note that if your other conditions are joined by an OR operation, the dummy condition would need to be inverted so that it always returns false.
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