CODEWITHSUNDEEP
c#.netsqlsqldatareader
Brian
Brian

Reputation: 25834

Casting SqlDataReaders

What are the advantages of replacing (int)reader[0] with reader.GetInt32(0)? I'm sure such casting functions are there for a reason, but other than it feeling more aesthetically pleasing to avoid the cast myself, I'm not sure what those reasons are.

Upvotes: 4

Views: 2360

Answers (3)

Liwen
Liwen

Reputation: 937

reader[0] returns an System.Object, (int)reader[0] is actually doing a cast from Object to Int32.

If you call GetXXX(0) methods, no conversions are performed. Therefore, the data retrieved from the stream must already be the type the method specified.

If the type of data retrieved doesn't match or the column has DBNull, it throws an InvalidCastException.

Upvotes: 1

StingyJack
StingyJack

Reputation: 19469

In code....

        void OneWay()
        {
            System.Data.SqlClient.SqlDataReader reader = null;
            int i = reader.GetInt32(0);
        }

        void OtherWay()
        {
            System.Data.SqlClient.SqlDataReader reader = null;
            int i = (int)reader[0];
        }

In IL

.method private hidebysig instance void OneWay() cil managed
{
    .maxstack 2
    .locals init (
        [0] class [System.Data]System.Data.SqlClient.SqlDataReader reader,
        [1] int32 i)
    L_0000: nop 
    L_0001: ldnull 
    L_0002: stloc.0 
    L_0003: ldloc.0 
    L_0004: ldc.i4.0 
    L_0005: callvirt instance int32 [System.Data]System.Data.Common.DbDataReader::GetInt32(int32)
    L_000a: stloc.1 
    L_000b: ret 
}


.method private hidebysig instance void OtherWay() cil managed
{
    .maxstack 2
    .locals init (
        [0] class [System.Data]System.Data.SqlClient.SqlDataReader reader,
        [1] int32 i)
    L_0000: nop 
    L_0001: ldnull 
    L_0002: stloc.0 
    L_0003: ldloc.0 
    L_0004: ldc.i4.0 
    L_0005: callvirt instance object [System.Data]System.Data.Common.DbDataReader::get_Item(int32)
    L_000a: unbox.any int32
    L_000f: stloc.1 
    L_0010: ret 
}

So, the IL is different, but I doubt that there is any noticeable difference between them. Maybe after a million iterations you will see the difference, but not likely.

Upvotes: 5

Joel Coehoorn
Joel Coehoorn

Reputation: 415810

The former can also accept the column name as a string rather than an index, and will attempt to cast the column value to an int. The latter only accepts the index and no casting will be performed.

Upvotes: 1

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