在XPO中实现sql中的函数功能

最近在项目中使用XPO时，遇到了这样的问题，在sql中有charindex方法
select * from table1 where charindex(col1, ';a;b;c;d;')<>0//col1 is a column in the table1
而在XPO中当我构造查询条件时却没有类似charindex的方法，后来在DevExpress的官方网站上提出了这样的问题，经过她们的帮助找到了实现charindex功能的方法。
以下是我的问题和她们的回复

Question：
By sql syntax, i can write this: select * from table1 where charindex(col1, ';a;b;c;d;')<>0 //col1 is a column in the table1
but in xpo,how can i realize this function( charindex('))?
if there have any way to do this, please help me.

thanks
Jet

Answered by Developer Express Team：

Hi Jet,

You can use the following code which creates a custom function:

class CustomCharIndexProvider : MSSqlConnectionProvider {
    public CustomCharIndexProvider(IDbConnection connection, AutoCreateOption autoCreateOption)
        : base(connection, autoCreateOption) {
    }
    public override string FormatFunction(FunctionOperatorType operatorType, params string[] operands) {
        if (operatorType == FunctionOperatorType.Custom && operands.Length == 3 && operands[0] == CharindexFunction.CharindexFunctionName)
            return String.Format("charindex({0}, {1})", operands[1], operands[2]);
        return base.FormatFunction(operatorType, operands);
    }
}
public class CharindexFunction : FunctionOperator {
    public const string CharindexFunctionName = "charindex";
    public CharindexFunction(CriteriaOperator expression1, CriteriaOperator expression2) : base(CharindexFunctionName, expression1, expression2) { }
}

Modify the Main function:
[STAThread]
static void Main() {
    string connectionString = ""; // You should specify the connection string to your database.
    XpoDefault.DataLayer = new SimpleDataLayer(new CustomCharIndexProvider(connectionString, AutoCreateOption.DatabaseAndSchema));
    
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(new Form1());
}

Using:
private void Form1_Load(object sender, EventArgs e) {
    // ...
    CriteriaOperator criteria = new CharindexFunction(expression1, expression2);
    XPCollection collection = new XPCollection(session1, objectType, criteria);
}

这里给大家分享一下，如果有类似的问题可以采用这种方法来解决。