/// <summary>
/// Creates a mapper Func for a projection.
/// </summary>
private Func <Row, T> CreateMapperForProjection <T>(RowSet rows, NewTypeProjection projection)
{
ICollection <Expression> methodBodyExpressions = new LinkedList <Expression>();
// The input parameter for our Func<Row, T>, a C* Row
ParameterExpression row = Expression.Parameter(CassandraRowType, "row");
// poco variable
ParameterExpression poco = Expression.Variable(typeof(T), "poco");
var constructorParameters = projection.ConstructorInfo.GetParameters();
var columnIndex = 0;
if (constructorParameters.Length == 0)
{
// Use default constructor
// T poco = new T()
methodBodyExpressions.Add(Expression.Assign(poco, Expression.New(projection.ConstructorInfo)));
}
else
{
var parameterExpressions = new List <Expression>();
if (constructorParameters.Length > rows.Columns.Length)
{
throw new IndexOutOfRangeException(string.Format("Expected at least {0} column(s), obtained {1}",
constructorParameters.Length, rows.Columns.Length));
}
for (columnIndex = 0; columnIndex < constructorParameters.Length; columnIndex++)
{
var c = rows.Columns[columnIndex];
var param = constructorParameters[columnIndex];
var getValueT = GetExpressionToGetColumnValueFromRow(row, c, param.ParameterType);
parameterExpressions.Add(getValueT);
}
// T poco = new T(param1, param2, ...)
methodBodyExpressions.Add(Expression.Assign(poco,
Expression.New(projection.ConstructorInfo, parameterExpressions)));
}
// Fill the rest of members with the rest of the column values
// ReSharper disable once GenericEnumeratorNotDisposed
var membersEnumerator = projection.Members.GetEnumerator();
while (membersEnumerator.MoveNext() && columnIndex < rows.Columns.Length)
{
var member = membersEnumerator.Current;
var c = rows.Columns[columnIndex];
var memberType = GetUnderlyingType(member);
var getColumnValue = GetExpressionToGetColumnValueFromRow(row, c, memberType);
// poco.SomeFieldOrProp = ... getColumnValue call ...
var getValueAndAssign = Expression.Assign(
Expression.MakeMemberAccess(poco, member), getColumnValue);
// Start with an expression that does nothing if the row is null
Expression ifRowValueIsNull = Expression.Empty();
// For collections, make an effort to return an empty collection instead of null
if (TryGetCreateEmptyCollectionExpression(c, memberType, out Expression createEmptyCollection))
{
// poco.SomeFieldOrProp = ... createEmptyCollection ...
ifRowValueIsNull = Expression.Assign(Expression.MakeMemberAccess(poco, member), createEmptyCollection);
}
var columnIndexExpression = Expression.Constant(columnIndex, IntType);
//Expression equivalent to
// if (row.IsNull(columnIndex) == false) => getValueAndAssign ...
// else => ifRowIsNull ...
methodBodyExpressions.Add(Expression.IfThenElse(
Expression.IsFalse(Expression.Call(row, IsNullMethod, columnIndexExpression)),
getValueAndAssign,
ifRowValueIsNull));
columnIndex++;
}
// The last expression in the method body is the return value, so put our new POCO at the end
methodBodyExpressions.Add(poco);
// Create a block expression for the method body expressions
var methodBody = Expression.Block(new [] { poco }, methodBodyExpressions);
// Return compiled expression
return(Expression.Lambda <Func <Row, T> >(methodBody, row).Compile());
}
protected override Expression VisitNew(NewExpression node)
{
Projection = new NewTypeProjection(node.Constructor);
return(node);
}