Entity Framework decimal rounding inconsistent in projection

Question

EF6 appears to be inconsistent in how it handles rounding when multiplying and adding integer columns with decimal values.

// CREATE TABLE MyTable (MyIntValue INT NOT NULL)
// INSERT INTO MyTable (MyIntValue) VALUES (10)
const int IntScale = 5;
const decimal DecimalScale = 5;
const decimal DecimalScale2 = 5.0m;
context.Set<MyTable>()
    .Select(row => new
    {
         WithFloats = 0.5f + (row.MyIntValue * 5.0f),                         // 50.5
         WithDecimals = 0.5m + (row.MyIntValue * 5.0m),                       // 51 
         WithDecimals2 = 0.5m + ((decimal)row.MyIntValue * 5.0m),             // 50.5            
         WithDecimals3 = 0.5m + ((decimal)row.MyIntValue * IntScale),         // 51
         WithDecimals4 = 0.5m + ((decimal)row.MyIntValue * (decimal)IntScale) // 51
         WithDecimals5 = 0.5m + ((decimal)row.MyIntValue * DecimalScale)      // 51
         WithDecimals6 = 0.5m + ((decimal)row.MyIntValue * DecimalScale2)     // 50.5
    })
    .Single();

Surely this isn't the expected/correct behaviour? I would expect the WithDecimals value to be 50.5 (not 51). Am I overlooking something simple? How can I ensure that WithoutDecimals doesn't get rounded without changing the type of the other constants?

The generated SQL for WithFloats and WithDecimals (respectively):

,CAST(0.5 AS REAL) + (CAST(MyIntValue AS REAL) * CAST(5 AS REAL)) AS WithFloats
,0.5 + (CAST(MyIntValue AS DECIMAL(19,0)) * CAST(5 AS DECIMAL(18))) AS WithDecimals

Answer 1

Explicitly define the column type, as well as the precision and scale of the decimal field by using a data-annotation

[Column(TypeName = "decimal(5,2)")]
public decimal MyDecimal { get; set; }

You can find the default LINQ-to-SQL CLR type mappings, which applies when using EF, here .

Read up on T-SQL numeric and decimal datatypes here .