How to Convert Integers to Strings in LINQ to Entities?

Challenges in converting integers to strings in LINQ to Entities

In LINQ to Entities, programmers may encounter difficulties when trying to convert integers in queries to strings. Conversions may result in errors, as in the following example:

var items = from c in contacts
            select new ListItem
            {
                Value = c.ContactId, // 无法隐式转换类型“int”（ContactId）到“string”（Value）。
                Text = c.Name
            };

An alternative is to use the ToString() method, which seems to be a possible solution:

var items = from c in contacts
            select new ListItem
            {
                Value = c.ContactId.ToString(), // 抛出异常：LINQ to Entities 不支持 ToString()。
                Text = c.Name
            };

However, this attempt also fails because LINQ to Entities does not support ToString(), thus generating an exception.

Overcoming conversion barriers in EF v4

EF v4 solves this conversion problem through the SqlFunctions.StringConvert method. This method provides a mechanism to convert a value to a string without explicit conversion. The following code demonstrates its usage:

var items = from c in contacts
            select new ListItem
            {
                Value = SqlFunctions.StringConvert((double)c.ContactId).Trim(),
                Text = c.Name
            };

Integers can be successfully converted to strings in LINQ to Entities by converting them to doubles in the StringConvert() parameter.

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