I need to pull values in similar tables from two different databases, combine them and then write the output to a CSV file. Can I just create a second connection string in the Properties file and explicitly pass the DataContext the second connection string for the other LINQ query? Or do I need to do something else? The tables are nearly identical except for an ID used for some criteria.
I've never used LINQ before but it seems the easier way to handle this insead of having to write SQL by hand.
if the schema matches both of the databases, then you should be able to just create second DataContext instance (giving it the second connection string as an argument). The LINQ to SQL doesn't check in any way whether you use "the right" database - if it has the right columns & tables it will work.
However, LINQ doesn't automatically work with multiple databases in any "smart" way, so it will need to download the content to the memory before doing any operations that involve multiple data sources. You can still use single LINQ query to do this - but you have to be careful about what part of it is running using in memory data. (By the way, you can use extension methods like "ToList" to explicitly say - get the data from the databse at this point).
You also mention that the tables are nearly identical except for an ID in some case - does that mean that primary/foreign keys are different? In that case, some autogenerated relations may not work. If it means that there is a different column name, then you could manually edit the generated schema to contain both columns and then use only the right one. However, this feels a bit odd - unless you're planning doing some manual edits to the schema, you could as well just generate two very similar schemas.
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I need to identify if a schema in database has any change in metadata such as changed table columns or changed procedure/package PL/SQL-codes additional/deleted triggers etc. I've tried to make a expdp with content=metadata_only and calculated a checksum of the dump. But this doesn't work because the checksum changes every time despite the same unchanged database. How to identify if a schema in database (its structure) has changed or not? Do I have to export the plain text metadata instead? Thx.
If you only need to know who did what when, use database auditing.
If you only need to know something might have changed, but don't care what and are okay with the possibility of the change not being significant, you can use the last_ddl_time from dba_objects and compare it to the last maximum value you got on the previous check. This can be done either at the schema or object level.
If you really do need to generate a delta and know for certain that something changed, you have two choices:
Construct data dictionary queries against all application dictionary views (lots of work, because there are lot of views - columns, tables, partitions, subpartitions, indexes, index partitions, index subpartitions, lobs, lob partitions, etc, etc, etc.)
(Recommended) Use dbms_metadata to extract the DDL of the entire schema. See this answer for a query that will export almost every object you would likely care about.
Either using #1 or #2, you can then compare old/new strings or use a hash function (e.g. dbms_crypto.hash) to compute a hash value and compare that. I wrote a schema upgrade tool that does exactly this - surgically identifies and upgrades individual objects that are different than some template source schema. I use dbms_metadata to look for diffs on the hash values. You will, however, need to set certain transforms to omit clauses you don't care about and that could have arbitrary changes, or mask them with regexp_replace after the fact (e.g. a sequence will contain the current value which will always be different.. you don't want to see this as a change). It can be a bit of work.
I have a lookup table that is harvested from the XML file and not physically stored in the MySQL database. Because of that all the data are represented in one word when it is queried out using jasper adhoc for example
ridikill
peon
thegreat
All these lookup should be like so
ridi kill
pe on
the great
how to make the data to show correctly in separate words.
You are going to have some trouble doing this exclusively in the Ad-Hoc editor, it simply doesn't have this kind of functionality on it's own. You could create a calculated field with the following code in the formula builder:
CaseWhen("RigType" == 'deepwaterdrillship', 'deep water drill ship', "RigType" == 'standardjackup', 'Standard Jack Up',"RigType"=='standardfloater','Standard Floater')
Replace all instances of "RigType" with your original field name. Obviously this will get quite manual if you have a lot of different strings.
If you created a calculated table in the domain/topic that you are using, with similar logic to the code above, this would be more powerful since you can join to your other tables. However, as Petter commented, this is a data source problem and in my experience it is always better to fix the source if possible.
My application will be querying a database using Entity Framework. The problem is that the database table structure changes fairly often (a few times a year).
Back in the SQL days, we would store SQL queries in Resource files (.resx) and when any database changes occurred, we could just edit the one resource file and not have to edit any code in the app, recompile, etc.
Are there any good ways to do this with Linq-to-SQL?
Linq2SQL is innately code-based. If your schema is going to change, then the code will need to change.
The only way I can see around this, and still get some of the benefits of linq, is to write everything as Stored Procedures, which you can than add as method to the linq DataContext.
Then, as long as the Name, input parameters and output columns remain the same, you can change what the SP is doing on the database and the code can stay the same.
I am currently using entity framework (.net 4) to read from a 3rd party database using LINQ statements. Unfortunately, at compile time i do not know from which table i will be reading - in fact, new tables can be added to this database after my application is compiled. The table name to read from will be passed as a string parameter to my method.
How should one approach this situation when the table name is not know at compile time? i cannot even add these tables to my data model since they might not yet exist. whilst i like the convenience of linq, i am after a simple approach.
thanks!
For the queries that can only be constructed at run-time and that will return types of different shapes, you're pretty much forced to craft and execute the SQL you want to run yourself. DataContext.ExecuteQuery(string query, params object[] parameters) is going to be your friend.
You probably would already do this, but I would recommend keeping this portion of code isolated to one section of the code, where you execute the query, and then put the results into an strongly typed object before exposing it to other area's of your application. Make sure you clean the table name too.
I've got two tables that need to be joined via LINQ, but they live in different databases. Right now I'm returning the results of one table, then looping through and retrieving the results of the other, which as you can guess isn't terribly efficient. Is there any way to get them into a single LINQ statement? Is there any other way to construct this to avoid the looping? I'm just looking for ideas, in case I'm overlooking something.
Note that I can't alter the databases, i.e. I can't create a view in one that references the other. Something I haven't tried yet is creating views in a third database that references both tables. Any ideas welcome.
You can do this, even across servers, as long as you can access one database from the other. That is, if it's possible to write a SQL statement against ServerA.DatabaseA that accesses ServerB.DatabaseB.schema.TableWhatever, then you can do the same thing in LINQ.
To do it, you'll need to edit the .dbml file by hand. You can do this in VS 2008 easily like this: Right-click, choose Open With..., and select XML Editor.
Look at the Connection element, which should be at the top of the file. What you need to do is provide an explicit database name (and server name, if different) for tables not in the database pointed to by that connection string.
The opening tag for a Table element in your .dbml looks like this:
<Table Name="dbo.Customers" Member="Customers">
What you need to do is, for any table not in the connection string's database, change that Name attribute to something like one of these:
<Table Name="SomeOtherDatabase.dbo.Customers" Member="Customers">
<Table Name="SomeOtherServer.SomeOtherDatabase.dbo.Customers" Member="Customers">
If you run into problems, make sure the other database (or server) is really accessible from your original database (or server). In SQL Server Management Studio, try writing a small SQL statement running against your original database that does something like this:
SELECT SomeColumn
FROM OtherServer.OtherDatabase.dbo.SomeTable
If that doesn't work, make sure you have a user or login with access to both databases with the same password. It should, of course, be the same as the one used in your .dbml's connection string.
Create a proc/view in your database.
Given your conditions, I don't think you can do this in one Linq statement. But you can join the results of your L2S queries into a Linq to Objects query.