如何在C# Switch表达式中动态生成带单引号的SQL查询条件

方法1：嵌套Switch表达式 #

直接在字符串插值中嵌入小型Switch表达式，动态生成带单引号的ActionType值，无需额外变量：

string myQuery = source switch
{
    LogEntryType.IsInsert => "SELECT * FROM Table1;",
    LogEntryType.IsDelete or LogEntryType.IsUpdate =>
        $@"SELECT {thingsToSelect} FROM Table1 t WHERE t.ActionType = {source switch 
        { 
            LogEntryType.IsDelete => "'Deleted'", 
            LogEntryType.IsUpdate => "'Updated'" 
        }}",
    _ => throw new NotImplementedException(),
};

方法2：字典映射 #

提前定义枚举与目标字符串的映射关系，代码更整洁，适合枚举值较多的场景：

var actionTypeMap = new Dictionary<LogEntryType, string>
{
    { LogEntryType.IsDelete, "'Deleted'" },
    { LogEntryType.IsUpdate, "'Updated'" }
};

string myQuery = source switch
{
    LogEntryType.IsInsert => "SELECT * FROM Table1;",
    LogEntryType.IsDelete or LogEntryType.IsUpdate =>
        $@"SELECT {thingsToSelect} FROM Table1 t WHERE t.ActionType = {actionTypeMap[source]}",
    _ => throw new NotImplementedException(),
};

方法3：枚举扩展方法 #

给LogEntryType添加扩展方法，语义化更强，复用性高：

public static class LogEntryTypeExtensions
{
    public static string ToActionTypeString(this LogEntryType type)
    {
        return type switch
        {
            LogEntryType.IsDelete => "'Deleted'",
            LogEntryType.IsUpdate => "'Updated'",
            _ => throw new NotImplementedException()
        };
    }
}

// 使用时
string myQuery = source switch
{
    LogEntryType.IsInsert => "SELECT * FROM Table1;",
    LogEntryType.IsDelete or LogEntryType.IsUpdate =>
        $@"SELECT {thingsToSelect} FROM Table1 t WHERE t.ActionType = {source.ToActionTypeString()}",
    _ => throw new NotImplementedException(),
};

注意：生产环境中建议使用参数化查询避免SQL注入风险，比如通过SqlCommand添加参数，而非直接字符串拼接。

内容的提问来源于stack exchange，提问作者Bohn