Create Dynamic LINQ BinaryExpression using data in related tables - linq

Question

I have an application where all queries are created dynamically based on a simple data message received by a WCF service. A data message is, put simply, a collection of columnname/column value pairs, with the addition of an operator, e.g. Equals, Less Than, etc.
Simple Data Message of ColumnName-Value-Operator
Name, Joe, Equals
Age, 35, Less Than
Occupation, Geek, Equals
Rate, 1000, Greater Than
etc...
I have been somewhat successfully using dynamic binary expressions based on the contents of the datamessage.
BinaryExpression expression = null;
ParameterExpression parameter = Expression.Parameter(typeof(MessageType), "p");
foreach (row in DataMessage)
{
BinaryExpression exp = DataLib.MakeQueryFilter(typeof(MessageType),
row.ColumnName,row.ColumnValue,column.DataOperator.ToString(), parameter);
expression = expression == null ? exp : Expression.AndAlso(expression, exp);
results = DataContext.MessageType.Where(Expression.Lambda<Func<Media, bool>>(expression, parameter));
}
public static BinaryExpression MakeQueryFilter(Type type, string propertyName, object value, string dataoperator, ParameterExpression parameter)
{
//var type = oType.GetType();
object queryvalue = null;
var property = type.GetProperty(propertyName);
Type propertyType = property.PropertyType;
if ((propertyType.IsGenericType) && (propertyType.GetGenericTypeDefinition() == typeof(Nullable)))
propertyType = propertyType.GetGenericArguments()[0];
// convert the value appropriately
if (propertyType == typeof(System.Int32))
queryvalue = Convert.ToInt32(value);
if (property.PropertyType == typeof(DateTime))
queryvalue = Convert.ToDateTime(value);
if (property.PropertyType == typeof(Double))
queryvalue = Convert.ToDouble(value);
if (property.PropertyType == typeof(String))
queryvalue = Convert.ToString(value);
if (property.PropertyType == typeof(Guid))
queryvalue = new Guid(value.ToString());
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var constantValue = Expression.Constant(queryvalue);
Type[] types = new Type[2];
types.SetValue(typeof(Expression), 0);
types.SetValue(typeof(Expression), 1);
var methodInfo = typeof(Expression).GetMethod(dataoperator, types);
var equality2 = (BinaryExpression)methodInfo.Invoke(null, new object[] { propertyAccess, constantValue });
return equality2;
}
The problem I am encountering is when I want to query through a relationship to a value in another table, and even go two->nth relationships deep. Something like this:
Name, Joe, Equals
Age, 35, Less Than
Jobs.Occupation, Geek, Equals
Jobs.Occupation.Salary.Rate, 1000, Greater Than
I have no problem writing the LINQ query by hand:
var results = from m in DataContext.MessageType
where m.Name == "Joe"
& m.Age == 35
& m.Jobs.Occupation == "Geek"
& m.Jobs.Occupation.Salaray.Rate >= 1000
select m;
Any pointers how I can dynamically create this query? Any help is greatly appreciated. Thanks.
Eric S.

Answer 1

Note the use of expanding PropertyAccess.
{
BinaryExpression expression = null;
ParameterExpression parameter = Expression.Parameter(typeof(DataContext.Table), "p");
string columns = "Relation1.Relation2.Column1";
string value = "ABC123";
BinaryExpression exp = MakeQueryFilter(typeof(DataContext.Table), columns,value,'Equal', parameter);
expression = expression == null ? exp : Expression.AndAlso(expression, exp);
results = DataContext.Table.Where(Expression.Lambda<Func<Table, bool>>(expression, parameter));
}
public static BinaryExpression MakeQueryFilter(Type type, string propertyNames, object value, string dataoperator, ParameterExpression parameter)
{
string[] acolumns = columns.Split('.');
var property = typeof (MediaEvent).GetProperty(acolumns[0]);
MemberExpression propertyAccess = Expression.MakeMemberAccess(parameter, property);
Type propertyType = property.PropertyType;
if ((propertyType.IsGenericType) && (propertyType.GetGenericTypeDefinition() == typeof(Nullable)))
propertyType = propertyType.GetGenericArguments()[0];
if (acolumns.Length > 1)
{
for (int i = 1; i < acolumns.Length; i++)
{
propertyAccess = Expression.MakeMemberAccess(propertyAccess, propertyAccess.Type.GetProperty(acolumns[i]));
}
}
object queryvalue = null;
// convert the value appropriately
if (propertyType == typeof(System.Int32))
queryvalue = Convert.ToInt32(value);
if (property.PropertyType == typeof(DateTime))
queryvalue = Convert.ToDateTime(value);
if (property.PropertyType == typeof(Double))
queryvalue = Convert.ToDouble(value);
if (property.PropertyType == typeof(String))
queryvalue = Convert.ToString(value);
if (property.PropertyType == typeof(Guid))
queryvalue = new Guid(value.ToString());
var constantValue = Expression.Constant(queryvalue);
Type[] types = new Type[2];
types.SetValue(typeof(Expression), 0);
types.SetValue(typeof(Expression), 1);
var methodInfo = typeof(Expression).GetMethod(dataoperator, types);
var equality2 = (BinaryExpression)methodInfo.Invoke(null, new object[] { propertyAccess, constantValue });
return equality2;
}

Answer 2

I had the same issue. Thanks for the answer! Very useful!
You wrote this:
caller
{
BinaryExpression expression = null;
ParameterExpression parameter = Expression.Parameter(typeof(DataContext.Table), "p");
string columns = "Relation1.Relation2.Column1";
string value = "ABC123";
BinaryExpression exp
= MakeQueryFilter(typeof(DataContext.Table),
columns,value,'Equal', parameter);
expression = expression == null ? exp : Expression.AndAlso(expression, exp);
results = DataContext.Table.Where(
Expression.Lambda<Func<Table, bool>>(expression, parameter));
}
public static BinaryExpression MakeQueryFilter(Type type, string propertyNames, object value, string dataoperator, ParameterExpression parameter)
{
string[] acolumns = columns.Split('.');
var property = typeof (MediaEvent).GetProperty(acolumns[0]);
MemberExpression propertyAccess = Expression.MakeMemberAccess(parameter, property);
Type propertyType = property.PropertyType;
if ((propertyType.IsGenericType) && (propertyType.GetGenericTypeDefinition() == typeof(Nullable)))
propertyType = propertyType.GetGenericArguments()[0];
if (acolumns.Length > 1)
{
for (int i = 1; i < acolumns.Length; i++)
{
propertyAccess = Expression.MakeMemberAccess(propertyAccess, propertyAccess.Type.GetProperty(acolumns[i]));
}
}
object queryvalue = null;
// convert the value appropriately
if (propertyType == typeof(System.Int32))
queryvalue = Convert.ToInt32(value);
if (property.PropertyType == typeof(DateTime))
queryvalue = Convert.ToDateTime(value);
if (property.PropertyType == typeof(Double))
queryvalue = Convert.ToDouble(value);
if (property.PropertyType == typeof(String))
queryvalue = Convert.ToString(value);
if (property.PropertyType == typeof(Guid))
queryvalue = new Guid(value.ToString());
var constantValue = Expression.Constant(queryvalue);
Type[] types = new Type[2];
types.SetValue(typeof(Expression), 0);
types.SetValue(typeof(Expression), 1);
var methodInfo = typeof(Expression).GetMethod(dataoperator, types);
var equality2 = (BinaryExpression)methodInfo.Invoke(null, new object[] { propertyAccess, constantValue });
return equality2;
}
Maybe better if you write this:
public static BinaryExpression MakeQueryFilter<T>(string propertyNames, object value, string dataoperator, ParameterExpression parameter) where T : class
{
string[] props = propertyNames.Split('.');
var property = typeof(T).GetProperty(props[0]);
MemberExpression propertyAccess = Expression.MakeMemberAccess(parameter, property);
if (props.Length > 1)
{
for (int i = 1; i < props.Length; i++)
{
property = propertyAccess.Type.GetProperty(props[i]);
propertyAccess = Expression.MakeMemberAccess(propertyAccess, property);
}
}
Type propertyType = property.PropertyType;
if ((propertyType.IsGenericType) && (propertyType.GetGenericTypeDefinition() == typeof(Nullable)))
propertyType = propertyType.GetGenericArguments()[0];
object queryvalue = null;
// convert the value appropriately
if (propertyType == typeof(System.Int32))
queryvalue = Convert.ToInt32(value);
if (property.PropertyType == typeof(DateTime))
queryvalue = Convert.ToDateTime(value);
if (property.PropertyType == typeof(Double))
queryvalue = Convert.ToDouble(value);
if (property.PropertyType == typeof(String))
queryvalue = Convert.ToString(value);
if (property.PropertyType == typeof(Guid))
queryvalue = new Guid(value.ToString());
var constantValue = Expression.Constant(queryvalue);
Type[] types = new Type[2];
types.SetValue(typeof(Expression), 0);
types.SetValue(typeof(Expression), 1);
var methodInfo = typeof(Expression).GetMethod(dataoperator, types);
var equality2 = (BinaryExpression)methodInfo.Invoke(null, new object[] { propertyAccess, constantValue });
return equality2;
}