我想用paremeter更改where子句。例如我有2个字符串变量。
string searchText="John";
string userField="Name"//it can be ID,UserName or Email
我想根据“string userField =”Name“/”
更改Users属性(a.Name)var a entities.Users
where a.Name==searchText //a.Name(Name) is declared in userField. It can be ID,UserName or Email
我的代码如下所示:
var users = new
{
total = 10,
page = page,
record = (entities.Users.Count()),
rows = (from user in entities.Users
select new
{
ID = user.ID,
Name = user.Name,
UserName = user.UserName,
UserType = user.Role.Name,
Email = user.Email,
CreatedDate = user.CreatedDate,
UpdatedDate = user.UpdatedDate
}).AsEnumerable().Select(m => new { ID = m.ID, Name = m.Name, UserName = m.UserName, Email = m.Email, UserType = m.UserType, CreatedDate = String.Format("{0:d/M/yyyy HH:mm:ss}", m.CreatedDate), UpdatedDate = String.Format("{0:d/M/yyyy HH:mm:ss}", m.UpdatedDate) }),
};
我怎么能用这个lambada表达式做到这一点?
答案 0 :(得分:3)
您可以尝试以下方法:
.Where(u => (userField == "ID" && u.Id == searchText)
|| (userField == "Name" && u.Name == searchText)
|| (userField == "Email" && u.Email == searchText)
)
答案 1 :(得分:2)
在这种情况下我更喜欢扩展方法语法,并且这样做:
IQueryable<User> query = entities.Users;
switch (userField)
{
case "ID":
int searchID;
if (int.TryParse(searchText, out searchID))
query = query.Where(u => u.ID == searchID);
else
query = query.Where(u => false);
break;
case "Name":
query = query.Where(u => u.Name == searchText);
break;
case "Email":
query = query.Where(u => u.Email == searchText);
break;
}
var users = new
{
total = 10,
page = page,
record = (entities.Users.Count()),
rows = (from user in query
select new
// etc.
)
};
答案 2 :(得分:1)
由于您想动态创建where子句,我建议您使用Dynamic LINQ。它允许您动态创建where子句。
答案 3 :(得分:1)
string searchText="John";
string userField= "Name";
/* I leave it as an exercixe to add the TypeConversion if Id is Int */
ParameterExpression pe = Expression.Parameter(typeof(User),"usr");
Expression left = Expression.Property(pe, typeof(User).GetProperty(userField));
Expression right = Expression.Constant(searchText);
Expression equ = Expression.Equal(left, right);
var whereExpr = Expression.Lambda<Func<User, bool>>(
equ,
new ParameterExpression[] { pe });
var a = entities.Users.Where(whereExpr);