I'm mapping a column in a DBML to a bit column in SQL Server. Which of the following should "Type" (not server data type) in the DBML be marked as:
Binary (System.Data.Linq.Binary)
boolean
byte
From the MSDN reference http://msdn.microsoft.com/en-us/library/ms177603.aspx, for bit on MSSQL
"The string values TRUE and FALSE can be converted to bit values: TRUE is converted to 1 and FALSE is converted to 0."
Going by that logic, I would use boolean for your mapping.
NOTE: This is a pretty commonly discussed question on forums, including stack overflow. I'm certain there is a more comprehensive answer available.
I found a more comprehensive answer:
C# Equivalent of SQL Server DataTypes
Related
I'm not being able to understand how is the data type geography in SQL server...
For example I have the following data:
0xE6100000010CCEAACFD556484340B2F336363BCA21C0
what I know:
0x is prefix for hexadecimal
last 16 numbers are longitude: B2F336363BCA21C0 (double of decimal format)
16 numbers before the last 16 are latitude: CEAACFD556484340 (double of decimal format)
4 first numbers are SRID: E610 (hexadecimal for WGS84)
what I don't understand:
numbers from 5 to 12 : 0000010C
what is this?
From what I read this seems linked to WKB(Well Known Binary) or EWKB(Extended Well Known Binary) anyway i was not abble to find a definition for EWKB...
And for WKB this is supposed to be geometry type (4-byte integer) but the value doesn't match with the Geometry types codes (this example is for one point coordinate)
Can you help to understand this format?
The spatial types (geometry and geography) in SQL Server are implemented as CLR data types. As with any such data types, you get a binary representation when you query the value directly. Unfortunately, it's not (as far as I know) WKB but rather whatever format Microsoft decided was best for their implementation. For us (the users), we should work with the published interface of methods that have been published by MS (for instance the geography method reference). Which is to say that you should only try to decipher the MS binary representation if you're curious (and not for actually working with it).
That said, if you need/want to work with WKB, you can! For example, you can use the STGeomFromWKB() static method to create a geography instance from WKB that you provide and STAsBinary() can be called on a geography instance to return WKB to you.
The Format spec can be found here:
https://msdn.microsoft.com/en-us/library/ee320529(v=sql.105).aspx
As that page shows, it used to change very frequently, but has slowed down significantly over the past 2 years
I am currently needing to dig into the spec to serialize from JVM code into a bcp file so that I can use SQLServerBulkCopy rather than plain JDBC to upload data into tables (it is about 7x faster to write a bcp file than using JDBC), but this is proving to be more complicated than what I originally anticipated.
After testing with bcp, you can upload geographies by specifying an off row format ( varchar(max) ) and store the well known text, SQL server will see this and assume you wanted a geography based on the WKT it sees.
In my case converting to nvarchar resolved the issue.
If you download a Excel file from your Database then "true" or "false" is saved as String. Does it look the same in a Database or are the Booleans converted to Strings for the Excel-Sheet?
If the booleans aren't saved as "String" (String with special properties) in a database: How are they saved, as integer (like 0 and 1)?
While this is database dependent, I'll provide the best possible answer for an unknown.
In mysql:
Bool, Boolean: These types are synonyms for TINYINT(1). A value of
zero is considered false. Non-zero values are considered true.
Otherwise, you can use TINYINT or bit datatype.
TINYINT is support by the vast majority of databases also.
So in Access you can choose the column data type "Yes/No" and it will ask you while typing in the information the option "Yes" and "No". Yet, I do not see any of that on SQL Server Management Studio from Microsoft, I've searched around and seen that "bit" is the type, but when I put bit and I go to add information it appears as a normal column to type information. Or should I know myself to put either 0 or 1?
Also, is 0 true or false?
SQL Server doesn't have a boolean data type. The closest approximation is the bit. But that is a numeric type, not a boolean type. In addition, it only supports 2 values - 0 or 1 (and one non-value, NULL).
However, SQL (standard SQL, as well as T-SQL dialect) describes a Three valued logic - TRUE, FALSE and UNKNOWN. So bit isn't actually the best if you need all 3 states.
When using it, you cannot use that value directly in an if statement for example:
IF CONVERT(bit, 0)
BEGIN
print 'Ok'
END
would not parse and end up in error. So, you would need to write it as below;
IF CONVERT(bit, 0) = 0
In MS SQL bit is equivalent to a boolean.
https://msdn.microsoft.com/en-us/library/ms177603.aspx
Here you can read more about.
1 would be the equivalent of Yes
0 would be the equivalent of No
NULL would be the equivalent of Undefined ( if that exists in Access )
in SQL Server the equivalent to boolean datatype is Bit. Bit can take values 0(false) or 1 (true). If you want to set a default value to your Bit field on creating the table you can set:
...
myBoolean Bit, default 1,
..
The ODP.NET provider raises an exception in IDataReader.GetValue()/GetValues() if the column type is NUMBER(x,y) such that it will overflow all .NET numeric types. So Dapper is unable to map such a column to a POCO property.
I have an Oracle stored procedure that uses a REF CURSOR output parameter to return 3-column records. Fundamentally all 3 are NUMBER(something), but the ODP.NET Oracle managed provider seems to decide what ODP.NET or .NET type to turn them into.
I've been having problems with Dapper's Query() mapping records from this sproc into POCOs. Perhaps it actually isn't my fault, for once - it seems when a column comes across as an ODP.NET type instead of a .NET type, Dapper fails. If I comment an offending column out of my POCO, everything works.
Here's a pair of rows to illustrate:
--------------------------------------------------------------------
RDWY_LINK_ID RLC_LINK_OSET SIGN
---------------------- ---------------------- ----------------------
1829 1.51639964279667746989761971196153763602 1
14380 578.483600357203322530102380288038462364 -1
The first column is seen in .NET as int, the second column as type OracleDecimal, and the third as decimal. The second one is the problem.
For example, removing Dapper for the moment and using vanilla ODP.NET to access these records thusly indicates the problem:
int linkid = (int)reader.GetValue(0);
decimal linksign = (decimal)reader.GetValue(2);
//decimal dlinkoffset = (decimal)reader.GetValue(1); //**invalid cast exception at at Oracle.ManagedDataAccess.Client.OracleDataReader.GetDecimal(Int32 i)**
//object olinkoffset = reader.GetValue(1); //**same**
//decimal dlinkoffset = reader.GetDecimal(1); //**same**
//object[] values = new object[reader.FieldCount];
//reader.GetValues(values); //**same**
OracleDecimal linkoffset = (OracleDecimal)reader.GetProviderSpecificValue(1); //this works!
double dblinkoffset = reader.GetDouble(1); //interesting, this works too!
//decimal dlinkoffset = linkoffset.Value; //overflow exception
dblinkoffset = linkoffset.ToDouble(); //voila
What little browsing and breakpointing I've done in Dapper's SqlMapper.cs file shows me that it is extracting data from the reader with GetValue()/GetValues(), as above, which fails.
Any suggestions how to patch Dapper up? Many thanks.
UPDATE:
Upon reflection, I RTFMed: Section 3, "Obtaining Data from an OracleDataReader Object" of the Oracle Data Provider for .NET Developer’s Guide which explains. For NUMBER columns, ODP.NET's OracleDataReader will try a sequence of .NET types from Byte to Decimal to prevent overflow. But a NUMBER may still overflow Decimal, giving an invalid cast exception if you try any of the reader's .NET type accessors (GetValue()/GetValues()), in which case you have to use the reader's ODP.NET type accessor GetProviderSpecificValue(), which gives you an OracleDecimal, and if it overflows a Decimal, its Value property will give you an overflow exception and your only recourse is to coerce it into a lesser type with one of OracleDecimal's ToXxx() methods.
But of course the ODP.NET type accessor is not part of the IDataReader interface used by Dapper to hold reader objects, so it seems that Dapper, by itself, is Oracle-incompatible when a column type will overflow all .NET types.
The question remains - do the smart folk know how to extend Dapper to handle this. It seems to me I'd need an extension point where I could provide implementation on how to use the reader (forcing it to use GetDouble() instead of GetValue(), or casting to OracleDataReader and calling GetProviderSpecificValue()) for certain POCO property or column types.
To avoid this issue i used:
CAST(COLUMN AS BINARY_DOUBLE)
or
TO_BINARY_DOUBLE(COLUMN)
In the Oracle types listed here it's described as:
64-bit floating point number. This datatype requires 9 bytes, including the length byte.
Most of the other number types used by Oracle are 22 bytes max, so this is as good as it gets for .NET
I am starting modifying my DB trought Netbeans. I am now creating a new column which must contain a boolean value, and that option is not shown on the Type list for the new coumn. Neither Bool or anything similar to boolean.
Which is the option I must select to create a boolean? I know this could be done with an integer value but as every Status field has been created till now as a Boolean, I'd like to keep it this way.
Netbeans Version 7.4
Many of the Database vendors do not support the boolean datatype in their implementations for the obvious reasons of 3-values logic: null, true, false which is not very convenient for a 2-logic datatype.
I suggest you use the int datatype treating anything but zero as true, or anything positive as true.
You can find other answers to similar questions here:
https://stackoverflow.com/questions/6518356/why-doesnt-oracle-support-boolean-datatype
Is there a boolean type in oracle databases?