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# Creating Custom Transaction Checks

## Creating Custom Transaction Checks for TheNewEconomy

Transaction checks in **TheNewEconomy (TNE)** are used to validate and enforce rules during economic transactions. These checks ensure transactions adhere to server rules, such as ensuring balances don't exceed limits or items meet specific criteria.

***

### Overview

#### What is a Transaction Check?

A **Transaction Check** is a validation step that runs during a transaction. It ensures that the transaction is valid based on predefined rules.

#### Registration

Custom transaction checks must be registered with the transaction manager:

```java
TNECore.eco().transaction().addCheck(new CustomTransactionCheck());
TNECore.eco().transaction().addCheck(new CustomTransactionCheck(), "custom_group");
```

***

### Steps to Create a Custom Transaction Check

#### Step 1: Implement the `TransactionCheck` Interface

Create a class that implements the `TransactionCheck` interface. Below is an example of a custom check that prevents transactions below a minimum amount.

```java
import net.tnemc.core.transaction.TransactionCheck;
import net.tnemc.core.transaction.Transaction;
import net.tnemc.core.transaction.TransactionParticipant;
import net.tnemc.core.account.holdings.modify.HoldingsModifier;
import net.tnemc.core.actions.EconomyResponse;
import net.tnemc.core.actions.response.GeneralResponse;
import org.jetbrains.annotations.NotNull;

import java.math.BigDecimal;

public class CustomMinimumAmountCheck implements TransactionCheck {

  @Override
  public String identifier() {
    return "min_amount";
  }

  @Override
  public EconomyResponse checkParticipant(Transaction transaction, @NotNull TransactionParticipant participant, HoldingsModifier modifier) {
    if (modifier.getAmount().compareTo(new BigDecimal("10.00")) < 0) {
      return new EconomyResponse(false, "Transaction amount must be at least 10.00!");
    }
    return GeneralResponse.SUCCESS;
  }
}
```

***

### Step 2: Register the Custom Check

After creating your check, register it with TNE's transaction manager:

```java
TNECore.eco().transaction().addCheck(new CustomMinimumAmountCheck());
```

You can also group checks under a custom group identifier for better organization:

```java
TNECore.eco().transaction().addCheck(new CustomMinimumAmountCheck(), "custom_group");
```

***

### Example: Default Checks in TNE

#### **MinimumBalanceCheck**

Ensures the account balance does not go below a minimum threshold.

```java
@Override
public String identifier() {
  return "minbal";
}

@Override
public EconomyResponse checkParticipant(Transaction transaction, @NotNull TransactionParticipant participant, HoldingsModifier modifier) {
  if (participant.getCombinedEnding().compareTo(currency.getMinBalance()) < 0) {
    return HoldingsResponse.MIN_HOLDINGS;
  }
  return GeneralResponse.SUCCESS;
}
```

#### **MaximumBalanceCheck**

Prevents transactions that would exceed the maximum allowed balance.

```java
@Override
public String identifier() {
  return "maxbal";
}

@Override
public EconomyResponse checkParticipant(Transaction transaction, @NotNull TransactionParticipant participant, HoldingsModifier modifier) {
  if (participant.getCombinedEnding().compareTo(currency.getMaxBalance()) > 0) {
    return HoldingsResponse.MAX_HOLDINGS;
  }
  return GeneralResponse.SUCCESS;
}
```

***

### Step 3: Grouping Checks

You can group checks using `TransactionCheckGroup` for easy management of related validations:

```java
TransactionCheckGroup customGroup = new TransactionCheckGroup("custom_group");
customGroup.addCheck("min_amount");
TNECore.eco().transaction().addCheckGroup(customGroup);
```

***

### Key Methods in `TransactionCheck`

| Method               | Description                                                                            |
| -------------------- | -------------------------------------------------------------------------------------- |
| `identifier()`       | Returns the unique identifier for the check.                                           |
| `checkParticipant()` | Validates the transaction for a specific participant and returns an `EconomyResponse`. |
| `process()`          | Executes the check for all participants in the transaction.                            |

***

### Notes

* **Unique Identifier**: Each check must have a unique identifier returned by `identifier()`.
* **Comprehensive Validation**: Use `checkParticipant()` to enforce custom rules for each transaction participant.
* **Organized Checks**: Use groups to organize and manage multiple related checks.

***

By creating and registering custom transaction checks, you can enforce complex and unique economic rules tailored to your server's needs.


---

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