问题
I was looking for a smart conversion between .Net System.Type and SqlDbType. What I found it was the following idea:
private static SqlDbType TypeToSqlDbType(Type t)
{
String name = t.Name;
SqlDbType val = SqlDbType.VarChar; // default value
try
{
if (name.Contains("16") || name.Contains("32") || name.Contains("64"))
{
name = name.Substring(0, name.Length - 2);
}
val = (SqlDbType)Enum.Parse(typeof(SqlDbType), name, true);
}
catch (Exception)
{
// add error handling to suit your taste
}
return val;
}
The code above is not really nice and is a code smell, which is why I wrote the following, naïve, not smart, but useful function, based on https://msdn.microsoft.com/en-us/library/cc716729(v=vs.110).aspx:
public static SqlDbType ConvertiTipo(Type giveType)
{
var typeMap = new Dictionary<Type, SqlDbType>();
typeMap[typeof(string)] = SqlDbType.NVarChar;
typeMap[typeof(char[])] = SqlDbType.NVarChar;
typeMap[typeof(int)] = SqlDbType.Int;
typeMap[typeof(Int32)] = SqlDbType.Int;
typeMap[typeof(Int16)] = SqlDbType.SmallInt;
typeMap[typeof(Int64)] = SqlDbType.BigInt;
typeMap[typeof(Byte[])] = SqlDbType.VarBinary;
typeMap[typeof(Boolean)] = SqlDbType.Bit;
typeMap[typeof(DateTime)] = SqlDbType.DateTime2;
typeMap[typeof(DateTimeOffset)] = SqlDbType.DateTimeOffset;
typeMap[typeof(Decimal)] = SqlDbType.Decimal;
typeMap[typeof(Double)] = SqlDbType.Float;
typeMap[typeof(Decimal)] = SqlDbType.Money;
typeMap[typeof(Byte)] = SqlDbType.TinyInt;
typeMap[typeof(TimeSpan)] = SqlDbType.Time;
return typeMap[(giveType)];
}
Does someone have idea of how to get the same result in a cleaner, better and nice way?
回答1:
Your approach is a good start, but populating that dictionary should only be done once, as Ian says in a comment.
There is a GIST here that is based on the same idea, although it doesn't convert between the same sets of types: https://gist.github.com/abrahamjp/858392
Caveat
I have a working example below, but you need to be aware that this approach does have a few problems. For example:
- For a
string
, how do you pick the correct one betweenChar
,NChar
,VarChar
,NVarChar
,Text
orNText
(or evenXml
, maybe)? - And for blobs like
byte[]
, should you useBinary
,VarBinary
orImage
? - For
decimal
,float
anddouble
, should you go forDecimal
,Float
,Money
,SmallMoney
orReal
? - For a
DateTime
, do you needDateTime2
,DateTimeOffset
,DateTime
, orSmallDateTime
? - Are you using
Nullable
types, likeint?
? Those should most likely give the sameSqlDbType
as the underlying type.
Also, just providing a Type
tells you nothing of other constraints, like field size and precision. Making the right decision is also about how the data is used in your application and how it is stored in the database.
The best thing to do is really to let an ORM do this for you.
Code
public static class SqlHelper
{
private static Dictionary<Type, SqlDbType> typeMap;
// Create and populate the dictionary in the static constructor
static SqlHelper()
{
typeMap = new Dictionary<Type, SqlDbType>();
typeMap[typeof(string)] = SqlDbType.NVarChar;
typeMap[typeof(char[])] = SqlDbType.NVarChar;
typeMap[typeof(byte)] = SqlDbType.TinyInt;
typeMap[typeof(short)] = SqlDbType.SmallInt;
typeMap[typeof(int)] = SqlDbType.Int;
typeMap[typeof(long)] = SqlDbType.BigInt;
typeMap[typeof(byte[])] = SqlDbType.Image;
typeMap[typeof(bool)] = SqlDbType.Bit;
typeMap[typeof(DateTime)] = SqlDbType.DateTime2;
typeMap[typeof(DateTimeOffset)] = SqlDbType.DateTimeOffset;
typeMap[typeof(decimal)] = SqlDbType.Money;
typeMap[typeof(float)] = SqlDbType.Real;
typeMap[typeof(double)] = SqlDbType.Float;
typeMap[typeof(TimeSpan)] = SqlDbType.Time;
/* ... and so on ... */
}
// Non-generic argument-based method
public static SqlDbType GetDbType(Type giveType)
{
// Allow nullable types to be handled
giveType = Nullable.GetUnderlyingType(giveType) ?? giveType;
if (typeMap.ContainsKey(giveType))
{
return typeMap[giveType];
}
throw new ArgumentException($"{giveType.FullName} is not a supported .NET class");
}
// Generic version
public static SqlDbType GetDbType<T>()
{
return GetDbType(typeof(T));
}
}
And this is how you would use it:
var sqlDbType = SqlHelper.GetDbType<string>();
// or:
var sqlDbType = SqlHelper.GetDbType(typeof(DateTime?));
// or:
var sqlDbType = SqlHelper.GetDbType(property.PropertyType);
回答2:
It appears that this sort of lookup table is already available, albeit not in System.Data
(or .Object
or .Type
) but rather in System.Web.
Project -> Add Reference -> System.Web -> OK
Then https://msdn.microsoft.com/en-us/library/system.data.sqldbtype(v=vs.110).aspx also says
When setting command parameters, the SqlDbType and DbType are linked. Therefore, setting the DbType changes the SqlDbType to a supporting SqlDbType.
So, this should theoretically work;)
using Microsoft.SqlServer.Server; // SqlDataRecord and SqlMetaData
using System;
using System.Collections; // IEnumerator and IEnumerable
using System.Collections.Generic; // general IEnumerable and IEnumerator
using System.Data; // DataTable and SqlDataType
using System.Data.SqlClient; // SqlConnection, SqlCommand, and SqlParameter
using System.Web.UI.WebControls; // for Parameters.Convert... functions
private static SqlDbType TypeToSqlDbType(Type t) {
DbType dbtc = Parameters.ConvertTypeCodeToDbType(t.GetTypeCodeImpl());
SqlParameter sp = new SqlParameter();
// DbParameter dp = new DbParameter();
// dp.DbType = dbtc;
sp.DbType = dbtc;
return sp.SqlDbType;
}
回答3:
Edit: I was thinking about and this works for System.Data.SqlTypes types. I'll leave it here just in case it helps someone in the future.
I do something like this:
object objDbValue = DbReader.GetValue(columnIndex);
Type sqlType = DbReader.GetFieldType(columnIndex);
Type clrType = null;
if (sqlType.Name.StartsWith("Sql"))
{
var objClrValue = objDbValue.GetType()
.GetProperty("Value")
.GetValue(objDbValue, null);
clrType = objClrValue.GetType();
}
Because every SqlDbType has a .Value property which is the actual underlying CLR type I use reflection to get it. It's too bad SqlDbType doesn't have some interface that would hold this .Value property and reflection wouldn't be needed.
It's not perfect but you don't have to manually create, maintain or populate a dictionary. You can just look up a type in an existing dict, and if it doesn't exist use the upper method to add the mapping automatically.
Pretty much auto-generated.
Also takes care of any new types that SQL Server might receive in the future.
回答4:
My office mate gave me the idea to try a property of SqlParameter:
Func<Object, SqlDbType> getSqlType = val => new SqlParameter("Test", val).SqlDbType;
Func<Type, SqlDbType> getSqlType2 = type => new SqlParameter("Test", type.IsValueType?Activator.CreateInstance(type):null).SqlDbType;
//returns nvarchar...
Object obj = "valueToTest";
getSqlType(obj).Dump();
getSqlType2(typeof(String)).Dump();
//returns int...
obj = 4;
getSqlType(obj).Dump();
getSqlType2(typeof(Int32)).Dump();
//returns bigint...
obj = Int64.MaxValue;
getSqlType(obj).Dump();
getSqlType2(typeof(Int64)).Dump();
https://dotnetfiddle.net/8heM4H
来源:https://stackoverflow.com/questions/35745226/net-system-type-to-sqldbtype