动态linq，如何生成LIKE和NOT LIKE

在我的场景中，我必须根据用户在屏幕上选择的内容构建动态查询。

用户可以选择列名，然后选择运算符，然后键入值。

我已经为了相同而做了它，但是LIKE和NOT LIKE的语法怎么样？ 所以

1。 我将列名添加到我的列表中

var columns = new Dictionary { {"CurrentStatus", "Current Status"}, {"RequestNumber", "Request Number"}, {"RequestDate", "Request Date"}, {"IsOnHold", "Is On Hold"}, {"BrandReturnedVehicle", "Brand Returned Vehicle"}, {"TypeReturnedVehicle", "Type Returned Vehicle"}, {"ChassisReturnedVehicle", "Chassis Returned Vehicle"}, {"DestructionCertificateNumberReturnedVehicle", "Destruction Certificate Number Returned Vehicle"}, {"AmmountWithVAT", "Ammount WithVAT "}, {"AmmountWithoutVat", "Ammount Without Vat"}, {"Percentage", "Percentage"}, {"VehicleDestructionDate", "Vehicle Destruction Date"}, {"Comments", "Comments"}, {"Discriminator", "Request Type"}, }; DdlColumn1.DataSource = columns; DdlColumn1.DataTextField = "Value"; DdlColumn1.DataValueField = "Key"; DdlColumn1.DataBind(); 

第2位。 根据所选的列名称，我将运算符添加到下拉列表中。

 protected void DdlColumn1SelectedIndexChanged(object sender, EventArgs e) { LoadOperatorsDependingOnColumn(sender as DropDownList, DdlColumn1.SelectedValue); } private void LoadOperatorsDependingOnColumn(DropDownList ddlOperators, string columnname) { var operators = new Dictionary(); operators.Clear(); switch (columnname) { case "CurrentStatus": AddTextOperatorsToList(operators); ddlOperators.DataSource = operators; ddlOperators.DataTextField = "Value"; ddlOperators.DataValueField = "Key"; ddlOperators.DataBind(); break; case "AmmountWithVat": AddNumberOperatorsToList(operators); break; } } private static void AddTextOperatorsToList(Dictionary operators) { operators.Add("==", "Equals"); operators.Add("", "Not Equals"); operators.Add("LIKE", "Contains"); operators.Add("NOT LIKE", "Does not Contain"); } private static void AddNumberOperatorsToList(Dictionary operators) { operators.Add("=", "Equals"); operators.Add("", "Not Equals"); operators.Add(">", "Greater than"); operators.Add(">=", "Greater or equal than"); operators.Add("<", "Less than"); operators.Add("<=", "Less or equal than"); } private string ColumnType(string columnName) { switch (columnName) { case "CurrentStatus": return "Text"; break; case "RequestNumber": return "Text"; break; } } private string BuildQuery() { var sb = new StringBuilder(); //var list = RequestBaseBL.GetRequestByCustomQuery("RequestNumber == \"12\""); if (ColumnType(DdlColumn1.SelectedValue) == "Text" && DdlOperator1.SelectedItem.Text=="==") { sb.Append(DdlColumn1.SelectedValue); sb.Append(DdlOperator1.SelectedValue); sb.Append("\"" + TxtValue1.Text + "\""); } 

1. 我不知道的是如何连接/追加字符串以使不等于，包含和不包含与动态linq libray一起使用

Answer 1

似乎动态linq的东西不支持’LIKE’ – 但我想这就是你问这个问题的原因。 我能想到的最好的方法是将LIKE替换成类似（x> = y0 AND x 所以：

 if (ColumnType(DdlColumn1.SelectedValue) == "Text" && DdlOperator1.SelectedItem.Text=="LIKE") { string s = TxtValue1.Text; Char c = s[s.Length - 1]; string s1 = s.Substring(0, s.Length - 1) + ((Char)(c + 1)); string clause = string.Format("{0} >= \"{1}\" and {0} < \"{2}\"", DdlColumn1.SelectedValue, s, s1); sb.Append(clause); } 

即将1添加到搜索字符串的最后一个字符的值，并将其用作搜索的上限。
如果你知道你只处理简单的拉丁字符，你可以使它更简单并使用：

 string clause = string.Format("{0} >= \"{1}\" and {0} <= \"{1}z\"", DdlColumn1.SelectedValue, TxtValue1.Text); 

但是在这里看一下谓词构建器以获得更多类型安全性可能是值得的。

编辑

嗯，我从来没有！ 忘记这一切。

看来你可以使用“myField.Contains（myCriteria）”和“myField.StartsWith（myCriteria）”进行CONTAINS和LIKE

 sb.Append(string.Format("{0}.Contains(\"{1}\")", DdlColumn1.SelectedValue, TxtValue1.Text); 

和

 sb.Append(string.Format("{0}.StartsWith(\"{1}\")", DdlColumn1.SelectedValue, TxtValue1.Text); 

而且，不喜欢：

 sb.Append(string.Format("!{0}.StartsWith(\"{1}\")", DdlColumn1.SelectedValue, TxtValue1.Text);